Cant purchase in app!:(

See especially the second paragraph under "Make an in-app purchase":

About in-app purchases - Apple Support

Hi

Go to iTunes main page bottom of page apple I'd click that view I'd Go to manage payments add / check your credit card details are correct and the 3 digit code from the back of the card.

If you don't have a credit card buy a iTunes gift card redeem at the bottom of iTunes main page.

Cheers

Brian 🇬-1F1E7;