We figured it out. I was a permissions issue.

Actually, the main retrieved list of mixins has "meta:globalLibVersion": "1.65.1" at the bottom but I still can't validate any of the mixins. I always get the error for the version, even though the mixin id came from that retrieved list of mixins with  "meta:globalLibVersion": "1.65.1". 

I’m working on cloning an existing schema. I successfully retrieved the target schema and created the cloned schema, but I’m encountering PES errors.While validating the mixins, the API consistently returns an error stating it expects version 1.65.1 of the mixins. However, the mixins returned by the...

You might need your credential name added to a role.For reference, you can view the video titled “Get the necessary attribute-based access control permissions”. Start at the 2:40 mark: https://experienceleague.adobe.com/en/docs/experience-platform/landing/platform-apis/api-authentication#get-abac-pe...