Pick x402 payment options on a supported network only

CHANGELOG.md

@@ -36,6 +36,7 @@ Argument completions for prompts and resource templates, tasks on MCP 2026-07-28
 
 ### Fixed
 
+- x402 payments no longer fail with "Unknown network" when a server lists a payment option on a chain mcpc cannot sign for (e.g. Solana) before the Base one: `x402 sign` and `--x402` sessions now pick the first option on a supported network. When there is none, the error lists what the server offered and which networks are supported.
 - `tools-call`, `prompts-get` and `completion-complete` no longer send arguments other than what you typed: a JSON array passed inline or on stdin is now rejected (MCP arguments must be an object), a `__proto__:=...` argument is no longer dropped, and a number too large to represent (e.g. `n:=1e400`) is kept as a string instead of being sent as `null`. (#448)
 - Bridge log rotation no longer races the file it rotates: under load the rename could run before the log file was opened or flushed, so the rotation was silently skipped and the first lines of the new file were lost.
 - Windows sessions no longer pile up duplicate bridge processes when `tasklist` is slow or unavailable. A liveness check that could not run used to report every bridge dead, so each command spawned a replacement without stopping the healthy original; the check now falls back to a signal probe, the old bridge is always asked to shut down, and a bridge that finds another one registered for its session exits on its own. (#427)

src/lib/x402/fetch-middleware.ts

@@ -30,6 +30,7 @@ import {
   signPayment,
   parsePaymentRequired,
   selectAcceptEntry,
+  isSupportedNetwork,
   DEFAULT_PAYMENT_EXPIRY_SECONDS,
   type SignerWallet,
   type PaymentRequiredAccept,
@@ -520,7 +521,8 @@ function extractToolCallName(body: RequestInit['body'] | undefined): string | un
  * Pick an accept entry from a tool's `_meta.x402` block honoring `schemePreference`.
  *
  * Prefers the spec-shaped `accepts[]` array when present; falls back to the flat fields
- * only when the preference matches the flat scheme (or the preference is `auto`).
+ * only when the preference matches the flat scheme (or the preference is `auto`) and the
+ * flat network is one mcpc can sign for.
  * Returning undefined defers signing to the 402 fallback path, which re-runs the
  * selector against the authoritative PAYMENT-REQUIRED header.
  */
@@ -540,6 +542,9 @@ function selectAcceptFromToolMeta(
   if (preference !== 'auto' && preference !== x402.scheme) {
     return undefined;
   }
+  if (!isSupportedNetwork(x402.network)) {
+    return undefined;
+  }
 
   return {
     scheme: x402.scheme,

src/lib/x402/signer.ts

@@ -127,6 +127,15 @@ const NETWORKS: Record<string, NetworkConfig> = {
   },
 };
 
+/**
+ * Whether mcpc can sign payments on the given network (CAIP-2 id, e.g. `eip155:8453`).
+ * Servers may offer the same price on several chains at once (Base, Solana, ...); only
+ * the networks in `NETWORKS` are supported.
+ */
+export function isSupportedNetwork(network: string): boolean {
+  return Object.hasOwn(NETWORKS, network);
+}
+
 // ---------------------------------------------------------------------------
 // Types
 // ---------------------------------------------------------------------------
@@ -221,14 +230,19 @@ function randomPermit2Nonce(): string {
 // ---------------------------------------------------------------------------
 
 function isValidExactAccept(a: PaymentRequiredAccept): boolean {
-  return a.scheme === 'exact' && Boolean(a.payTo && a.amount && a.network && a.asset);
+  return (
+    a.scheme === 'exact' &&
+    Boolean(a.payTo && a.amount && a.network && a.asset) &&
+    isSupportedNetwork(a.network)
+  );
 }
 
 function isValidUptoAccept(a: PaymentRequiredAccept): boolean {
   return (
     a.scheme === 'upto' &&
     Boolean(a.payTo && a.amount && a.network && a.asset) &&
-    Boolean(a.extra?.facilitatorAddress)
+    Boolean(a.extra?.facilitatorAddress) &&
+    isSupportedNetwork(a.network)
   );
 }
 
@@ -238,6 +252,9 @@ function isValidUptoAccept(a: PaymentRequiredAccept): boolean {
  * - `auto`   → prefer valid `upto`, fallback to valid `exact`
  * - `upto`   → require valid `upto`; undefined if none
  * - `exact`  → require valid `exact`; undefined if none
+ *
+ * Entries on networks mcpc cannot sign for (see `isSupportedNetwork`) are skipped, so a
+ * server that lists a Solana option before the Base one still gets a Base payment.
  */
 export function selectAcceptEntry(
   accepts: PaymentRequiredAccept[],
@@ -291,9 +308,10 @@ export function parsePaymentRequired(
   const accept = selectAcceptEntry(header.accepts, schemePreference);
   if (!accept) {
     const requested = schemePreference === 'auto' ? 'exact or upto' : schemePreference;
-    const available = header.accepts.map((a) => a.scheme).join(', ');
+    const offered = header.accepts.map((a) => `${a.scheme} on ${a.network}`).join(', ');
     throw new ClientError(
-      `No valid "${requested}" scheme found in PAYMENT-REQUIRED accepts. Available: ${available}`
+      `No valid "${requested}" scheme on a supported network found in PAYMENT-REQUIRED accepts. ` +
+        `Offered: ${offered}. Supported networks: ${Object.keys(NETWORKS).join(', ')}`
     );
   }
 

test/unit/lib/x402/fetch-middleware.test.ts

@@ -338,6 +338,18 @@ describe('extractAcceptFromPaymentRequired', () => {
     const result = extractAcceptFromPaymentRequired(uptoOnly, 'exact');
     expect(result).toBeUndefined();
   });
+
+  it('skips entries on networks mcpc cannot sign for', () => {
+    const solanaFirst = {
+      x402Version: 2,
+      accepts: [
+        { ...EXACT_ACCEPT, network: 'solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp' },
+        EXACT_ACCEPT,
+      ],
+    };
+    const result = extractAcceptFromPaymentRequired(solanaFirst, 'exact');
+    expect(result?.accept.network).toBe(EXACT_ACCEPT.network);
+  });
 });
 
 // ---------------------------------------------------------------------------

test/unit/lib/x402/signer.test.ts

@@ -94,6 +94,16 @@ const VALID_UPTO_ACCEPT: PaymentRequiredAccept = {
   },
 };
 
+// Apify's x402 endpoints offer the same price on Base and on Solana; mcpc signs EVM only.
+const SOLANA_EXACT_ACCEPT: PaymentRequiredAccept = {
+  scheme: 'exact',
+  network: 'solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp',
+  amount: '1000000',
+  asset: 'EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v',
+  payTo: 'ECUPkq6DP8VUSEueL4qNznyNDJLwu6PQhnMQ5cuZsTLH',
+  maxTimeoutSeconds: 60,
+};
+
 const MOCK_WALLET: SignerWallet = {
   privateKey: '0x1234567890abcdef',
   address: MOCK_ADDRESS,
@@ -166,6 +176,28 @@ describe('selectAcceptEntry', () => {
     const result = selectAcceptEntry([VALID_EXACT_ACCEPT, secondExact], 'auto');
     expect(result?.amount).toBe('1000000');
   });
+
+  it('exact: skips entries on unsupported networks', () => {
+    const result = selectAcceptEntry([SOLANA_EXACT_ACCEPT, VALID_EXACT_ACCEPT], 'exact');
+    expect(result?.network).toBe('eip155:84532');
+  });
+
+  it('upto: skips entries on unsupported networks', () => {
+    const solanaUpto = { ...VALID_UPTO_ACCEPT, network: SOLANA_EXACT_ACCEPT.network };
+    const result = selectAcceptEntry([solanaUpto, VALID_UPTO_ACCEPT], 'upto');
+    expect(result?.network).toBe('eip155:84532');
+  });
+
+  it('auto: prefers a supported exact over an upto on an unsupported network', () => {
+    const solanaUpto = { ...VALID_UPTO_ACCEPT, network: SOLANA_EXACT_ACCEPT.network };
+    const result = selectAcceptEntry([solanaUpto, VALID_EXACT_ACCEPT], 'auto');
+    expect(result?.scheme).toBe('exact');
+  });
+
+  it('returns undefined when every entry is on an unsupported network', () => {
+    const result = selectAcceptEntry([SOLANA_EXACT_ACCEPT], 'auto');
+    expect(result).toBeUndefined();
+  });
 });
 
 // ---------------------------------------------------------------------------
@@ -227,6 +259,21 @@ describe('parsePaymentRequired', () => {
     expect(() => parsePaymentRequired(b64, 'upto')).toThrow(ClientError);
     expect(() => parsePaymentRequired(b64, 'upto')).toThrow('upto');
   });
+
+  it('picks the Base entry when a Solana entry is listed first', () => {
+    const b64 = buildPaymentRequired([SOLANA_EXACT_ACCEPT, VALID_EXACT_ACCEPT]);
+    const { accept } = parsePaymentRequired(b64, 'auto');
+    expect(accept.network).toBe('eip155:84532');
+  });
+
+  it('throws naming the offered and the supported networks when none is supported', () => {
+    const b64 = buildPaymentRequired([SOLANA_EXACT_ACCEPT]);
+    expect(() => parsePaymentRequired(b64, 'exact')).toThrow(ClientError);
+    expect(() => parsePaymentRequired(b64, 'exact')).toThrow(
+      'exact on solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp'
+    );
+    expect(() => parsePaymentRequired(b64, 'exact')).toThrow('Supported networks: eip155:8453');
+  });
 });
 
 // ---------------------------------------------------------------------------