Hey @Eden,
I would still recommend having a chat with the licensing team to see what they can work out for you, If you are using n8n as a backend and collecting user credentials to interact with other services that are not yours then it will need a license although we have been known to make exceptions so it is always worth finding out.
It sounds like you might need to use the API to create the credential in n8n once you have the token, I made a quick node on this here: Google credentials stop working after a while - #13 by Jon which may help.