Error: account validation failed: AA21 didn’t pay prefund

I have been using mintNFT.js file from backend. But facing issue and getting message as
**"account validation failed: AA21 didn't pay prefund"**.

I have checked in Biconomy (https://forum.biconomy.io/t/error-account-validation-failed-aa21-didnt-pay-prefund/419) Forum it shows might be the issues with smart contract or method whitelisting, however all the configured as per the expectation.

Can you please suggest some another way ?

Start with mintNFT.js in the backend and reproduce the “AA21 didn't pay prefund” error. Compare the configured smart contract and method whitelisting with the linked Biconomy forum discussion; done means identifying the configuration or contract cause and documenting a working path.

Written by the indexing model from the issue text.