I have set up everything for my clients to be able to register to my Authy application via scanning a QR code. The only thing is the QR code seems to be invalid and the reason is that I've done everything related to the JWT correct but I've missed one thing. The JW token must be signed with the application's production API key. However, I have no idea where or how to do this.
Twilio developer evangelist here.
Your production API key is available in the settings for your Authy application within the Twilio console.
As for how to sign the JWT with that token, you might have provide the code and information about any libraries that you are using to generate the JWT.