Ruby self signed JWT - INVALID_ACCESS_TOKEN

I was trying to generate self signed token with ‘jwt’ and ‘json-jwt’ gems and I always get “INVALID_ACCESS_TOKEN” error.
The rest of the application is good, because if I generate token with python sample and reuse it here, everything works fine.
Any idea what can be wrong? My JWT payload:

{
    "exp" => 1558531389,
    "iat" => 1558531089,
    "iss" => "urn:aid:my_number_here",
    "sub" => "urn:aid:my_number_here",
    "aud" => "https://services.poynt.net",
    "jti" => "d0c1e025-bcb1-49bc-a4bb-bf92f800938a"
}

Im able to encode and decode this with RS256 correctly. So I have no idea why server is declining it.