Hi Randal,
I’m afraid the very nature of access tokens is that they expire, and a non-expiring token is not desirable as it introduces a security risk. All is not lost however, as when you receive an access token you will also get a refresh token which can be used in future to obtain further access tokens as they expire.
https://dev.freeagent.com/docs/oauth#the-access-token-request
Your app will need to either refresh the access token periodically before it expires, or handle responses after the access token has already expired (using the refresh token to obtain a new access token and reattempting the original request).
Currently access tokens expire every 7 days however this is something we’re looking at reducing to further improve our users’ security, so we’d strongly recommend any integrations make provision for this from the outset.
Hope that helps,
Paul.