"Please check that the File/Reference and the Tax ID of the taxpayer correct"

This error usually occurs when you are trying to respond to a request from the general option "Respond to requests or submit documentation related to a notification received from AEAT " inappropriately or when entering incorrect data.

The error appears after clicking "OK" to try to move on from "Step 1: Generating the request" to "Step 2: "Sign and submit the application."

Check the notification you received to see what literal options are offered in the notification and whether or not a specific path is specified to respond to it.

Also remember that from the "Electronic Registration" option you can access the different options contemplated for responding to requests.