Prezzycard is .. Stupid. Website borked, no interest in fixing it.

Amazed that even 3 years later, nothing's changed.

... so which sign-in button do I press?

For future reference, the right hand one of the two is the correct one. This is what you get if you click the left one - a screenshot I took >6 months ago:

Of note, Tweets from 2012:

... their whole process has been broken for at least 3 years and hasn't changed.

This years Tweets: