fix(transaction-controller): strip gasPrice for fee-market transactions instead of rejecting

packages/transaction-controller/CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- Strip redundant `gasPrice` from fee-market transactions (type `0x2`/`0x4`) instead of rejecting them, fixing compatibility with RPCs that return both `gasPrice` and EIP-1559 fields (e.g. Arbitrum) ([#7877](https://github.com/MetaMask/core/issues/7877))
+
 ### Added
 
 - Add optional `submissionMethod` property and `TransactionSubmissionMethod` enum to `TransactionMeta` ([#8375](https://github.com/MetaMask/core/pull/8375))

packages/transaction-controller/src/utils/validation.test.ts

@@ -315,6 +315,56 @@ describe('validation', () => {
         );
       });
 
+      it('strips gasPrice instead of throwing when type is fee-market and EIP-1559 fields are present', () => {
+        const txParams = {
+          from: FROM_MOCK,
+          to: TO_MOCK,
+          gasPrice: '0x01',
+          maxFeePerGas: '0x02',
+          maxPriorityFeePerGas: '0x01',
+          type: TransactionEnvelopeType.feeMarket,
+          // TODO: Replace `any` with type
+          // eslint-disable-next-line @typescript-eslint/no-explicit-any
+        } as any;
+
+        expect(() => validateTxParams(txParams)).not.toThrow();
+        expect(txParams.gasPrice).toBeUndefined();
+        expect(txParams.maxFeePerGas).toBe('0x02');
+      });
+
+      it('strips gasPrice instead of throwing when type is setCode and EIP-1559 fields are present', () => {
+        const txParams = {
+          from: FROM_MOCK,
+          to: TO_MOCK,
+          gasPrice: '0x01',
+          maxFeePerGas: '0x02',
+          maxPriorityFeePerGas: '0x01',
+          type: TransactionEnvelopeType.setCode,
+          // TODO: Replace `any` with type
+          // eslint-disable-next-line @typescript-eslint/no-explicit-any
+        } as any;
+
+        expect(() => validateTxParams(txParams)).not.toThrow();
+        expect(txParams.gasPrice).toBeUndefined();
+      });
+
+      it('still throws if gasPrice and EIP-1559 fields are present but no explicit type', () => {
+        expect(() =>
+          validateTxParams({
+            from: FROM_MOCK,
+            to: TO_MOCK,
+            gasPrice: '0x01',
+            maxFeePerGas: '0x01',
+            // TODO: Replace `any` with type
+            // eslint-disable-next-line @typescript-eslint/no-explicit-any
+          } as any),
+        ).toThrow(
+          rpcErrors.invalidParams(
+            'Invalid transaction params: specified gasPrice but also included maxFeePerGas, these cannot be mixed',
+          ),
+        );
+      });
+
       it('throws if gasPrice, maxPriorityFeePerGas or maxFeePerGas is not a valid hexadecimal string', () => {
         expect(() =>
           validateTxParams({

packages/transaction-controller/src/utils/validation.ts

@@ -353,9 +353,28 @@ function validateParamChainId(
 /**
  * Validates gas values.
  *
+ * Some RPC providers (e.g. Arbitrum's eth_fillTransaction) return both
+ * gasPrice and EIP-1559 fee fields. When the envelope type is explicitly
+ * fee-market (0x2/0x4), strip the redundant gasPrice before validating
+ * mutual exclusivity, matching the normalization already done elsewhere
+ * in the codebase (GasFeePoller, updateGasFees, retry utils).
+ *
  * @param txParams - The transaction parameters to validate.
  */
 function validateGasFeeParams(txParams: TransactionParams): void {
+  const type = txParams.type as TransactionEnvelopeType | undefined;
+
+  // When the envelope type explicitly indicates a fee-market transaction,
+  // strip gasPrice rather than rejecting — some RPCs return both fields.
+  if (
+    txParams.gasPrice &&
+    (txParams.maxFeePerGas || txParams.maxPriorityFeePerGas) &&
+    type &&
+    TRANSACTION_ENVELOPE_TYPES_FEE_MARKET.includes(type)
+  ) {
+    delete txParams.gasPrice;
+  }
+
   if (txParams.gasPrice) {
     ensureProperTransactionEnvelopeTypeProvided(txParams, 'gasPrice');
     ensureMutuallyExclusiveFieldsNotProvided(