I had similar issue
10.10.2022 13:06:56.751 *ERROR* [[0:0:0:0:0:0:0:1] [1665421616748] POST /services/accesstoken/verify HTTP/1.1] org.apache.sling.servlets.post.impl.operations.ModifyOperation Exception during response processing.
org.apache.sling.api.resource.PersistenceException: Resource at '/services/accesstoken/verify' is not modifiable.
I fixed it by putting services here:![sling-servlet-resolver.png sling-servlet-resolver.png](https://experienceleaguecommunities.adobe.com/t5/image/serverpage/image-id/51425iD3C5603E3113E29B/image-size/large/is-moderation-mode/true?v=v2&px=999)
It worked but after a while I started getting your error