Thanks. The problem is that there is no place to enter any credit card details on my phone - it was pretty much a blank screen. When I logged in using my details on the iPhone, there were boxes to enter the details.
I just did it on my son's iPhone easily. On my Samsung there was nowhere to enter the details....the whole section was missing. However I think he is now logged in as me. Oh well.
I'm trying to check in on the app but it won't let me add a card in the onboard expenses section and I can't move forward with check-in without adding.