Ah, I didn't realise it was still in test mode.
I've clicked on the first challenge in Level 2, and I got the message about not being charged as it's in test mode. I clicked to continue, and it is picking up a default email address and asking me for a Google password. Above that is the word 'Paypal' which is cut off. Does this want my PayPal email address and password? Or some other password?
I've tried entering the password that goes with the Gmail account it's showing, but it doesn't like that. I can't enter my PayPal password, as the email address is not my PayPal one and it won't let me change it.
So, I clicked on 'Forgot password' and went through the process of creating a new one with the email address that was showing. That all seemed to be successful, so I clicked back on the SSiSpanish app and it told me it had had a problem and asked me to send an error report, which I did.
After that, I went back into SSiSpanish and clicked to Buy Level 2 Challenge 1, went through with the new password, and everything worked fine. The lesson is playing!