The payload forms the actual data (also known as a claim) stored in the JWT. According to your application's requirements, you can put any number of claims into your JWT payload component. There are some predefined claims, such as iss (issuer), sub (subject), exp (expiration time), iat (issued at), and so on, that can be used, but all of these are optional:

{
 "sub": "1234567890",
 "username": "Test User",
 "iat": 1516239022
}