If you generate e-way bills or e-invoices from code, you will meet the same handful of error codes again and again. The messages are terse, the codes sometimes arrive with a stray comma ("301,"), and a couple of them mean the opposite of what a retry loop assumes.

This is the list I wish I had when I started. Every code below is one I actually hit against the live network, not one I copied from a PDF.

The ones you will see first

108: Invalid login credentials

The API username or password was refused. It is almost never a typo. The common causes:

The API user was created for a different GSP (for example inside your accounting software). An API user only works with the GSP it was created for.

The password has special characters. Letters and digits only is the safe choice.

You sent your normal portal login instead of the API user.

Fix: create a fresh API user for the GSP you are calling through (e-way bill portal: Registration, then For GSP).…