hi
Do I have to create a new app token every time it expires or how can I refresh it?
Hi, 
Not necessarily. There’s a refresh token that allows you to perform the update.
See the documentation:
Refreshing Access Tokens
This is incorrect.
The Client Credential OAuth flow (ie, App tokens) does NOT give you a refresh token as there’s no need for App tokens to be refreshed. By design with that OAuth flow when a token expires you just make the same POST request to get another as you did originally.