I would try something like this:

Set tRequest.Https = 1

Set tRequest.SSLCheckServerIdentity = 0

Set tRequest.SSLConfiguration = "ISC.FeatureTracker.SSL.Config"

How did you define $$$BASE64URLENCODE?

I see there is a difference between base64 and base64url encoding ...

url - String based data encoding: Base64 vs Base64url - Stack Overflow
 

I added this line in my code:

Set jwt = $Translate(jwt,"+/=","-_")