There are two cases where you will get this error.
Case 1: It might be due to using the wrong set of credentials. To resolve this issue, ensure that you are using the correct set of credentials.
Warning:Your GSP(GST Suvidha Provider) credentials are different from your IRP website login credentials.
Case 2: You might have missed adding the prefix ‘API_’ before your username. This prefix distinguishes API-specific credentials of Production environment users from those of sandbox environment users. Please ensure that you enter the username with the prefix.
Note:If you are a sandbox environment user, you do not need to include the prefix.
You can also refer to our help documentation to learn how to connect your Zoho Books organisation with IRP.
Books
Simplify accounting
and GST filing.