Thank you for reaching out!
The usual cause for receiving an invalid JWT ( opaque token ) is that the audience parameter was not specified, or not done so correctly. You will need to pass the audience parameter in the token request, specifying the recipient, which should then return the Access Token in JWT format. Documentation for reference :
With regards to the Knowledge Article still being up to date, short answer should be yes, but to be safe, we will follow it from scratch and see if we happen to encounter any issues which might need to get addressed. If something comes up, we will update the Knowledge Article as soon as possible. Thank you for checking in with us on the matter!
Hope this helped!
Gerald