Hello, Grandmountainadventure.
I understand that you have been unable to complete an in-app purchase within the Grand Mountain Adventure game. I’m glad to help you get those resorts unlocked.
To complete an in-app purchase, your Apple ID must have a payment method associated with it that includes enough funds to cover the purchase. You will find the instructions needed to add a new payment method in the Apple Support article, Change, add, or remove Apple ID payment methods.
If you currently have a payment method and "something is wrong with the primary payment method that you have on file, a different payment method will be charged. Learn about how purchases are billed." You can find more information in the article, If your payment method is declined in the App Store or iTunes Store.
I hope this helps.
Best Regards.