Hello @pro2a and welcome to the Community!
This is an issue that appears semi-frequently in the Community. It may be helpful to first take a look at our How to Setup OAuth for Existing Magento 2 Integrations article to ensure you’ve accurately updated your existing Magento 2 integration from API credential authentication to the new OAuth workflow.
Additionally, here are some Community threads that have addressed similar issues, where other members have found solutions:
As my colleague David mentioned in that first linked thread, issues like these are directly related to your integration, so it may be helpful to reach out to our wonderful Support colleagues who can potentially point you in the correct direction by identifying any blatant integration issues.
I hope this helps, and thanks for being a Community member!
-Brian