The below steps should help solve most of this issue:

1) Access your Papaya Play account by going to the website and clicking on your Account name on the top right. Select “My Account”.
2) If you have not verified your email address, there should be a message at the top that says “PLEASE VERIFY YOUR EMAIL ADDRESS”.
3) Click on “Edit” of your email, where it will show the current email you are using for your account. Next to it, you should see the button “Resend”. Click “Resend”.
4) This will resend your account verification email again. Once you receive it, follow its instructions to verify your email address.

After that, you should now be able to purchase from the Pop-Up Shop.