diff --git a/BACKEND_CHANGES.md b/BACKEND_CHANGES.md
index cac0f13..965ef6d 100644
--- a/BACKEND_CHANGES.md
+++ b/BACKEND_CHANGES.md
@@ -39,6 +39,33 @@ Response:
 
 ---
 
+## 1.1. `GET /fastcheck` — добавить `amount` в ответ
+
+Фронт автоматически делает `GET /fastcheck` после ввода полного номера
+(`xxxx-xxxx-xxxx`), чтобы показать получателю сумму до ввода кода. Сейчас в
+`api.txt` ответ содержит только `fastcheck`, `expiration`, `Status` — суммы нет.
+
+Добавить:
+
+```diff
+GET /fastcheck
+Body: { "fastcheck": "1234-5678-0001" }
+Response:
+{
+  "fastcheck": "1234-5678-0001",
+  "expiration": "2026-07-07T09:08:18Z",
++ "amount": 158000,
++ "currency": "RUB",
++ "note": "За кофе",
+  "Status": true
+}
+```
+
+Также: GET с телом — нестандарт, многие HTTP-клиенты его выкидывают. **Принимать
+`?fastcheck=...` как query-параметр** (фронт шлёт оба варианта одновременно).
+
+---
+
 ## 2. Зафиксировать единицу `amount`
 
 В `api.txt` пример `"amount": 158000` неоднозначен. Зафиксировать:
@@ -144,6 +171,8 @@ Body:
 - [ ] DNS + HTTPS + CORS (блокер)
 - [ ] `orderId`, `note`, `returnUrl` в `POST /fastcheck` (create)
 - [ ] `note` возвращается в `GET /fastcheck`
+- [ ] `amount` (+ currency) возвращается в `GET /fastcheck`
+- [ ] `GET /fastcheck` принимает `?fastcheck=` как query-param
 - [ ] Зафиксировать `amount` в основной единице (рубли)
 - [ ] Webhook на `fastcheck.paid` с HMAC-подписью
 - [ ] Гранулярные ошибки accept
diff --git a/src/app/app.routes.ts b/src/app/app.routes.ts
index 783e2be..dbccfc8 100644
--- a/src/app/app.routes.ts
+++ b/src/app/app.routes.ts
@@ -3,8 +3,14 @@
 export const routes: Routes = [
   {
     path: '',
-    loadComponent: () =>
-      import('./pages/fastcheck-page/fastcheck-page').then((m) => m.FastcheckPage)
+    loadComponent: () => {
+      // Branch: ?id=<orderId> means legacy SBP merchant flow.
+      const hasLegacyId = typeof window !== 'undefined'
+        && new URLSearchParams(window.location.search).has('id');
+      return hasLegacyId
+        ? import('./pages/legacy-pay-page/legacy-pay-page').then((m) => m.LegacyPayPage)
+        : import('./pages/fastcheck-page/fastcheck-page').then((m) => m.FastcheckPage);
+    }
   },
   {
     path: 'new',
diff --git a/src/app/pages/fastcheck-page/fastcheck-page.html b/src/app/pages/fastcheck-page/fastcheck-page.html
index bac2f41..5f64f61 100644
--- a/src/app/pages/fastcheck-page/fastcheck-page.html
+++ b/src/app/pages/fastcheck-page/fastcheck-page.html
@@ -25,10 +25,11 @@
             type="text"
             class="input"
             [ngModel]="fastcheckNumber()"
-            (ngModelChange)="fastcheckNumber.set($event)"
+            (ngModelChange)="onNumberChange($event)"
             placeholder="1234-5678-0001"
             inputmode="numeric"
             autocomplete="off"
+            maxlength="14"
           />
           <a class="btn btn--ghost" routerLink="/new" aria-label="Создать новый fastCHECK">Новый</a>
         </div>
@@ -49,8 +50,12 @@
             step="1"
             inputmode="numeric"
             placeholder="0"
+            [readonly]="amountLoading() || fastcheckAmount() !== null"
           />
         </div>
+        @if (amountLoading()) {
+          <span class="field__hint">Проверяем…</span>
+        }
       </div>
 
       <!-- Code -->
@@ -61,10 +66,10 @@
           type="text"
           class="input"
           [ngModel]="fastcheckCode()"
-          (ngModelChange)="fastcheckCode.set($event)"
-          placeholder="0000"
+          (ngModelChange)="onCodeChange($event)"
+          placeholder="00000"
           inputmode="numeric"
-          maxlength="8"
+          maxlength="5"
           autocomplete="one-time-code"
         />
         @if (error()) {
@@ -72,7 +77,7 @@
         }
       </div>
 
-      <button class="pay-btn" type="button" (click)="pay()">
+      <button class="pay-btn" type="button" (click)="pay()" [disabled]="!canPay()">
         <span class="pay-btn__icon">
           <svg width="20" height="20" viewBox="0 0 24 24" fill="none" stroke="currentColor"
                stroke-width="2.5" stroke-linecap="round" stroke-linejoin="round">
diff --git a/src/app/pages/fastcheck-page/fastcheck-page.ts b/src/app/pages/fastcheck-page/fastcheck-page.ts
index 9b17a16..cae540c 100644
--- a/src/app/pages/fastcheck-page/fastcheck-page.ts
+++ b/src/app/pages/fastcheck-page/fastcheck-page.ts
@@ -13,6 +13,13 @@ interface WebSessionResponse {
   Status: boolean;
 }
 
+interface CheckFastcheckResponse {
+  fastcheck: string;
+  amount?: number;
+  expiration: string;
+  Status: boolean;
+}
+
 @Component({
   selector: 'app-fastcheck-page',
   imports: [FormsModule, RouterLink],
@@ -31,6 +38,7 @@ export class FastcheckPage {
   fastcheckAmount = signal<number | null>(null);
   fastcheckCode = signal<string>('');
   error = signal<string>('');
+  amountLoading = signal<boolean>(false);
 
   popupOpen = signal<boolean>(false);
   popupLoading = signal<boolean>(false);
@@ -38,6 +46,13 @@ export class FastcheckPage {
   webSessionId = signal<string>('');
   paid = signal<boolean>(false);
   private pollHandle: ReturnType<typeof setInterval> | null = null;
+  private lastLookedUpNumber = '';
+
+  canPay = computed(() => {
+    const digits = this.fastcheckNumber().replace(/\D/g, '');
+    const codeDigits = this.fastcheckCode().replace(/\D/g, '');
+    return digits.length === 12 && codeDigits.length === 5 && !this.amountLoading();
+  });
 
   telegramLink = computed(() => {
     const sid = this.webSessionId();
@@ -62,12 +77,7 @@ export class FastcheckPage {
   }
 
   pay(): void {
-    if (!this.fastcheckNumber().trim()) {
-      this.error.set('Введите номер');
-      return;
-    }
-    if (!this.fastcheckCode().trim()) {
-      this.error.set('Введите код');
+    if (!this.canPay()) {
       return;
     }
     this.error.set('');
@@ -168,4 +178,64 @@ export class FastcheckPage {
   onAmountChange(value: number | null): void {
     this.fastcheckAmount.set(value);
   }
+
+  /** Mask fastcheck number as XXXX-XXXX-XXXX, allow only digits. */
+  onNumberChange(raw: string): void {
+    const digits = (raw ?? '').replace(/\D/g, '').slice(0, 12);
+    const groups: string[] = [];
+    for (let i = 0; i < digits.length; i += 4) {
+      groups.push(digits.slice(i, i + 4));
+    }
+    const masked = groups.join('-');
+    this.fastcheckNumber.set(masked);
+    this.error.set('');
+
+    // If number became incomplete, drop the previously fetched amount so the
+    // user doesn't see a stale value tied to a different (now-edited) number.
+    if (digits.length < 12 && this.lastLookedUpNumber) {
+      this.fastcheckAmount.set(null);
+      this.lastLookedUpNumber = '';
+    }
+
+    // Auto-lookup when 12 digits are entered (and we haven't already looked it up).
+    if (digits.length === 12 && masked !== this.lastLookedUpNumber) {
+      this.lookupFastcheck(masked);
+    }
+  }
+
+  /** Allow only digits, max 5, in the code field. */
+  onCodeChange(raw: string): void {
+    const digits = (raw ?? '').replace(/\D/g, '').slice(0, 5);
+    this.fastcheckCode.set(digits);
+    this.error.set('');
+  }
+
+  private lookupFastcheck(number: string): void {
+    this.lastLookedUpNumber = number;
+    this.amountLoading.set(true);
+    this.fastcheckAmount.set(null);
+
+    // GET /fastcheck — body in GET is non-standard; many HTTP libs strip it.
+    // The backend should accept ?fastcheck= as a query param too. We send both.
+    this.http
+      .request<CheckFastcheckResponse>('GET', `${FASTCHECK_API}/fastcheck`, {
+        body: { fastcheck: number },
+        params: { fastcheck: number }
+      })
+      .subscribe({
+        next: (res) => {
+          this.amountLoading.set(false);
+          if (res?.Status && typeof res.amount === 'number') {
+            this.fastcheckAmount.set(res.amount);
+          } else if (res?.Status === false) {
+            this.error.set('Платёж не найден или просрочен.');
+          }
+        },
+        error: () => {
+          this.amountLoading.set(false);
+          this.error.set('Не удалось проверить номер. Попробуйте ещё раз.');
+          this.lastLookedUpNumber = '';
+        }
+      });
+  }
 }
diff --git a/src/app/pages/legacy-pay-page/legacy-pay-page.html b/src/app/pages/legacy-pay-page/legacy-pay-page.html
new file mode 100644
index 0000000..3538cd7
--- /dev/null
+++ b/src/app/pages/legacy-pay-page/legacy-pay-page.html
@@ -0,0 +1,78 @@
+<div class="page">
+  <div class="card">
+
+    <div class="card__header">
+      <div class="sbp-logo">
+        <img src="https://sbp.nspk.ru/storage/settings/common/logo/0645d335-8b62-43a1-9a33-0d4c9d1dc0e0.svg"
+             alt="СБП" />
+      </div>
+      <h1 class="card__title">Оплата через СБП</h1>
+      <p class="card__subtitle">Система быстрых платежей</p>
+    </div>
+
+    <div class="card__body">
+
+      <div class="field">
+        <label class="field__label" for="amount">Сумма платежа</label>
+        <div class="input-wrap" [class.input-wrap--error]="error()">
+          <span class="input-wrap__prefix">₽</span>
+          <input
+            id="amount"
+            type="number"
+            class="input-wrap__input"
+            [ngModel]="amount()"
+            (ngModelChange)="onAmountChange($event)"
+            min="1"
+            step="1"
+            inputmode="numeric"
+            placeholder="0"
+            autofocus
+          />
+        </div>
+        @if (error()) {
+          <span class="field__error">{{ error() }}</span>
+        }
+      </div>
+
+      <div class="currency-badge">
+        <span class="currency-badge__flag">🇷🇺</span>
+        <span class="currency-badge__code">RUB</span>
+        <span class="currency-badge__name">Российский рубль</span>
+      </div>
+
+      <div class="field">
+        <label class="field__label" for="note">Примечание</label>
+        <textarea
+          id="note"
+          class="note-input"
+          [ngModel]="note()"
+          (ngModelChange)="onNoteChange($event)"
+          placeholder="Причина платежа..."
+          rows="3"
+          maxlength="500"
+        ></textarea>
+      </div>
+
+      <button class="pay-btn" type="button" (click)="pay()" [disabled]="loading()">
+        <span class="pay-btn__icon">
+          <svg width="20" height="20" viewBox="0 0 24 24" fill="none" stroke="currentColor"
+               stroke-width="2.5" stroke-linecap="round" stroke-linejoin="round">
+            <rect x="1" y="4" width="22" height="16" rx="2" ry="2" />
+            <line x1="1" y1="10" x2="23" y2="10" />
+          </svg>
+        </span>
+        {{ loading() ? 'Подождите...' : 'Перейти к оплате' }}
+      </button>
+    </div>
+
+    <div class="card__footer">
+      <span class="secure-badge">
+        <svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor"
+             stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
+          <path d="M12 22s8-4 8-10V5l-8-3-8 3v7c0 6 8 10 8 10z" />
+        </svg>
+        Защищённое соединение
+      </span>
+    </div>
+  </div>
+</div>
diff --git a/src/app/pages/legacy-pay-page/legacy-pay-page.scss b/src/app/pages/legacy-pay-page/legacy-pay-page.scss
new file mode 100644
index 0000000..498d511
--- /dev/null
+++ b/src/app/pages/legacy-pay-page/legacy-pay-page.scss
@@ -0,0 +1,60 @@
+@use './../../../shared' as *;
+
+.sbp-logo {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  background: rgba(255, 255, 255, 0.15);
+  backdrop-filter: blur(8px);
+  border-radius: 16px;
+  padding: 12px 20px;
+  border: 1px solid rgba(255, 255, 255, 0.25);
+  margin-bottom: 14px;
+
+  img {
+    height: 40px;
+    display: block;
+
+    @media (max-width: 480px) {
+      height: 34px;
+    }
+  }
+}
+
+.currency-badge {
+  display: flex;
+  align-items: center;
+  gap: 10px;
+  background: #f1f5f9;
+  border-radius: 12px;
+  padding: 12px 16px;
+  margin-bottom: 18px;
+
+  &__flag { font-size: 22px; line-height: 1; }
+  &__code { font-size: 15px; font-weight: 700; color: #0f172a; }
+  &__name { font-size: 13px; color: #64748b; margin-left: auto; }
+}
+
+.note-input {
+  width: 100%;
+  border: 2px solid #e2e8f0;
+  border-radius: 14px;
+  background: #f8fafc;
+  padding: 14px 16px;
+  font-size: 15px;
+  font-weight: 500;
+  color: #0f172a;
+  font-family: inherit;
+  resize: vertical;
+  outline: none;
+  transition: border-color 0.2s, box-shadow 0.2s, background 0.2s;
+  line-height: 1.5;
+
+  &::placeholder { color: #cbd5e1; font-weight: 400; }
+
+  &:focus {
+    border-color: #2563eb;
+    box-shadow: 0 0 0 4px rgba(37, 99, 235, 0.12);
+    background: #fff;
+  }
+}
diff --git a/src/app/pages/legacy-pay-page/legacy-pay-page.ts b/src/app/pages/legacy-pay-page/legacy-pay-page.ts
new file mode 100644
index 0000000..0800580
--- /dev/null
+++ b/src/app/pages/legacy-pay-page/legacy-pay-page.ts
@@ -0,0 +1,91 @@
+import { Component, computed, inject, signal } from '@angular/core';
+import { FormsModule } from '@angular/forms';
+import { ActivatedRoute } from '@angular/router';
+import { HttpClient } from '@angular/common/http';
+
+interface LegacyPayResponse {
+  payload?: string;
+}
+
+/**
+ * Legacy SBP merchant payment flow.
+ * Activated when the root URL has `?id=<orderId>`.
+ * Mirrors public/payment.html behaviour:
+ *   POST https://qr.vitanova.network:567/qr
+ *   { payment, amount, currency, id, note } -> { payload: '<sbp-deep-link>' }
+ *   then window.location.href = payload.
+ */
+@Component({
+  selector: 'app-legacy-pay-page',
+  imports: [FormsModule],
+  templateUrl: './legacy-pay-page.html',
+  styleUrl: './legacy-pay-page.scss'
+})
+export class LegacyPayPage {
+  private http = inject(HttpClient);
+  private route = inject(ActivatedRoute);
+
+  private readonly LEGACY_API = 'https://qr.vitanova.network:567/qr';
+
+  amount = signal<number | null>(null);
+  note = signal<string>('');
+  error = signal<string>('');
+  loading = signal<boolean>(false);
+
+  paymentId = signal<string>('');
+
+  canPay = computed(() => {
+    const a = this.amount();
+    return !!this.paymentId() && a !== null && a > 0 && !this.loading();
+  });
+
+  constructor() {
+    const id = this.route.snapshot.queryParamMap.get('id') ?? '';
+    this.paymentId.set(id);
+  }
+
+  onAmountChange(value: number | null): void {
+    this.amount.set(value);
+    if (this.error()) this.error.set('');
+  }
+
+  onNoteChange(value: string): void {
+    this.note.set(value);
+  }
+
+  pay(): void {
+    if (!this.canPay()) {
+      if (!this.paymentId()) {
+        this.error.set('Не указан идентификатор платежа (параметр id)');
+      } else {
+        this.error.set('Введите корректную сумму');
+      }
+      return;
+    }
+    this.error.set('');
+    this.loading.set(true);
+
+    const body = {
+      payment: 'sbp',
+      amount: this.amount(),
+      currency: 'rub',
+      id: this.paymentId(),
+      note: this.note().trim()
+    };
+
+    this.http.post<LegacyPayResponse>(this.LEGACY_API, body).subscribe({
+      next: (res) => {
+        this.loading.set(false);
+        if (res?.payload) {
+          window.location.href = res.payload;
+        } else {
+          this.error.set('Сервер не вернул ссылку для оплаты.');
+        }
+      },
+      error: () => {
+        this.loading.set(false);
+        this.error.set('Ошибка при создании платежа. Попробуйте ещё раз.');
+      }
+    });
+  }
+}
diff --git a/src/shared.scss b/src/shared.scss
index 7d6922e..f6b3fa5 100644
--- a/src/shared.scss
+++ b/src/shared.scss
@@ -114,6 +114,14 @@
     color: #ef4444;
     font-weight: 500;
   }
+
+  &__hint {
+    display: block;
+    margin-top: 6px;
+    font-size: 13px;
+    color: #64748b;
+    font-weight: 500;
+  }
 }
 
 .input-wrap {
@@ -191,6 +199,7 @@
   transition: opacity 0.15s, transform 0.1s, box-shadow 0.15s;
   box-shadow: 0 6px 20px rgba(37, 99, 235, 0.38);
   font-family: inherit;
+  appearance: none;
   -webkit-appearance: none;
 
   &:hover { opacity: 0.92; box-shadow: 0 8px 28px rgba(37, 99, 235, 0.45); }
@@ -212,17 +221,18 @@
 }
 
 // ─── Brand wordmark: "fastCHECK" inline ─────────────────────────────────────
-// "fast" is rendered half the size of "CHECK".
+// "fast" sits a bit smaller and lighter than "CHECK".
 .brand {
   display: inline-flex;
   align-items: baseline;
-  font-weight: 800;
+  font-weight: inherit;
   letter-spacing: -0.02em;
   white-space: nowrap;
+  font-size: calc(1em + 3px);
 
   &__fast {
-    font-size: 0.5em;
-    font-weight: 700;
+    font-size: 0.72em;
+    font-weight: 400;
     text-transform: lowercase;
     margin-right: 0.05em;
     opacity: 0.85;
@@ -230,6 +240,7 @@
 
   &__check {
     font-size: 1em;
+    font-weight: 500;
     text-transform: uppercase;
     letter-spacing: 0.02em;
   }