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This guide covers common issues when sending sponsored userOperations with CDP Paymaster and how to debug them.
For a complete list of error codes and their meanings, see the Errors page.

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Transaction Rejected by Policy

Symptom: Your userOperation is rejected before reaching the chain. Common causes:
  • Contract address not in your allowlist
  • Function not allowlisted for the contract
  • Per-user or global spend limits exceeded
  • Sender address doesn’t have required attestation
Solution: Check your Paymaster Configuration in CDP Portal:
  1. Verify the contract address is in your allowlist
  2. Confirm the specific function you’re calling is allowed
  3. Review your spend limits in the Configuration tab

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Execution Reverted

Symptom: The userOperation made it onchain but the transaction reverted. This means the smart contract execution failed. Common causes:

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Debugging with Tenderly

Tenderly is useful for simulating and debugging userOperations. To debug gas issues:
  1. Go to Tenderly and select the Entrypoint contract: 0x5ff137d4b0fdcd49dca30c7cf57e578a026d2789
  2. Use the simulateHandleOp function
  3. Paste your userOperation in the op field (wrap it in array brackets [{...}])
Tenderly Entrypoint simulation
To debug contract logic:
  1. Enter your smart contract’s address
  2. Paste the callData from your userOperation
  3. Run the simulation to see where it fails
Tenderly contract debugging
Having your contract verified on Basescan makes debugging much easier.

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Decoding Revert Data

If you see an error like:
Use an ABI decoder to decode the error:
  1. Upload your contract’s ABI
  2. Paste the data field
  3. The decoder will show the specific error and parameters

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Invalid Chain ID

Symptom: Request rejected with chain ID mismatch error. Cause: You’re using a Paymaster URL for a different network than your transaction targets. Solution: In CDP Portal, check the network dropdown in the top right corner and ensure it matches your transaction’s chain:
  • Base Mainnet — Chain ID 8453
  • Base Sepolia — Chain ID 84532
Network selection in CDP Portal

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Invalid Signature

Symptom: Error message about account signature or paymaster signature check failing.
Cause: The userOperation was modified after the Paymaster signed it. The Paymaster signs the complete userOperation. If you change any field after calling getPaymasterData(), the signature becomes invalid. Solution:
  1. Finalize all userOperation fields (callData, gas limits, etc.) before requesting the Paymaster signature
  2. Don’t modify the userOperation after receiving paymasterAndData
  3. If you need to change something, request a new Paymaster signature
When batching multiple userOperations, ensure each one has its own matching Paymaster signature. Signatures are not interchangeable between operations.

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Sponsorship Not Applied

Symptom: Transaction goes through but user paid gas instead of sponsorship. Common causes:
  • Wallet doesn’t support paymaster capabilities
  • paymasterService capability not passed correctly
  • Using an EOA instead of a smart account
Solution:
  1. Verify you’re using a smart account (check with eth_getCode — should return non-empty)
  2. Confirm the wallet supports paymasterService capability
  3. Check that you’re passing the paymaster URL in the correct format for your SDK

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Still Stuck?

If you’ve tried the above and are still having issues:
  1. Check the Logs tab in CDP Portal for detailed request/response data
  2. Export your userOp logs for offline analysis
  3. Reach out in CDP Discord in the #paymaster channel — include your error message, userOperation details, and what you’ve tried