How to loop a refresh_token call?

Hi everyone!

I am trying to make an API call in Power Query, for which I need an access_token. This is the script I use to get this access_token: 

The response from the script is an access_token, which expires in 10 minutes, and a refresh_token. I can use the refresh_token to make another call, for another access_token. I enter my initial refresh_token in the script above. But I am looking for a way that the next time the script refreshes, it uses the refresh_token from the previous call. Because the refresh_token is no longer valid after calling once.

I have looked into storing the called refresh_token into a parameter, but could not figure it out. Anyone knows how to fix my problem? Many thanks in advance!