wss://[ENDPOINT]/websockets?Authorization=Bearer%[TOKEN]&Client-Application=EPL
So again, this is wrong. You should have something like Bearer%20[TOKEN], not Bearer%[TOKEN].
I suspect this % comes from the value you’re injecting with ${access_token} and that you’re missing the whitespace between Bearer and the value.
If you think the issue in not on your side but with Gatling (which I don’t think), please provide a reproducer as instructed.