Hey @alex2020 welcome to the community!
I just glanced at your tenant and it looks like http://localhost:5268/ is indeed registered properly in Auth0. It sounds like this is the access token you are getting via auth0-react in your own app? Have you attempted to reproduce using the sample app? I just created an API with the same identifier and am getting a valid non-opaque access token back in the sample app. I recommend giving it a go as it will remove any application specific variables that might be in play here.
Let us know!