Right, you're still not giving anyone enough information to help you though. IE, what version of the Turnitin impl are you running? There are several versions, without knowing which one you're running, it's hard to understand the problem.

Also, can you turn on logging for the Turintin packages, there me be important information being missed in the logs.

Without more information it's impossible to know what's going on; I'm not able to reproduce this issue given the limited information you've passed on.

Maybe there is some difference between a fresh DB and the DB you're using that can shed light on what is happening.

Regardless, in order to debug this, there needs to be more information given.

I have already mentioned in provided description that "We have verified that all the user details are provided completely and this same API is working with Fresh mySQL Database". Please be informed that Firstname, Lastname, Email and other details of the users are completely filled in SAKAI but still we are unable to fetch Reports.
We are using URL API for Turnitin Integration.

"The user details are incomplete or invalid"

This error means the user's email address, first name and/or last name is not provided. These are required fields for Turnitin. You need to give the user the required information before they can submit to and receive original reports from Turnitin.

The follow sakai.properties will send dummy values for first and last name if not provided:

However, an email address will still be required. This is not a bug; this is a requirement from Turnitin.

Please verify that the user has the required data. Also, you might want to turn on some loggers for the Turnitin packages so you can see what is happening in the logs.

There's not much info to go on here, so it's hard to do analysis.

Also, which version of the Turnitin impl are you using?