Sandbox app setup


We’re starting work on an integration with a client’s existing bookings management system. I was going through the instructions on the docs (the quick start guide) for setting up a sandbox account and app and then authorising that app through Google’s OAuth playground. However, once I entered text in the scope field and went to authorise the app I got a 503 error initially. Multiple retries finally got a log on to appear but when I enter my sandbox email and password it just says that the email and password I entered was incorrect. Not sure where to go from there, or if I’m just missing something obvious.