"authorized user" on a credit card and holder does not pay it.

[Imackenzie]

What happens if you are an "authorized user" on a credit card and the person who has the card in their name stops making payments?

The credit rating agencies know that you are an authorized user, and have noted that on your credit report.

Does that have any effect on your credit rating? Are you in any way responsible for making payments?

"Authorized users receive credit cards that are connected to the primary cardholder's line of credit, but they are not responsible for paying off the charges they make on those cards. The person whose name is on the credit account is fully responsible for all charges made to the card.Jun 20, 2023."

You were not repsponible for the debt no matter what the collection agency creeps said. On the other hand, unless you set it up correctly you may have your credit score impacted. Frankly as someone retired for 7 years I don't give a hoot about my credit score. The only thing it is good for at this point in my life is travel rewards on new credit cards and they are getting less and less valuable.