Most probably this error happened because you had generated an ApplePay certificate using the Paytabs merchant profile which is not the same profile that initiated the payment.

In this article you will be going to know about: 

How to investigate the reason that caused this error?

You can investigate the reason for such an error from the "API debug log", by navigating to the Developer’s menu > Testing > API Debug Logs (within your desired profile).

Reason #1: The Uploaded certificate doesn't match the profile generated it in the first place.

To manage the ApplePay certificate in your Paytabs dashboard, you have to:

1. Generate a certificate (on the Paytabs side)

2. Upload the certificate to the ApplePay side3. Generate a certificate on the ApplePay side and download it

4. Upload the generated from step (3) to Paytabs Dashboard

For more details, check the article How to configure Apple Pay Certificate in my PayTabs dashboard? 

Steps (1) and (4) should be done using the same Paytabs merchant profile. if it doesn't match, you would receive the error "Profile mismatch"

The solution for that is to follow the steps (as mentioned above) in the article again And to use the same Profile on downloading the generated certificate, and on uploading the ApplePay one.