\'Your purchase could not be completed

Hello.

After a long time, I bought an iTunes gift card for $15 and charged it to my account.

I tried to make an in-app payment in the game,

\'Your purchase could not be completed.\' is displayed and payment cannot be made.

I kept trying again and waiting for hours, but to no avail.

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I'm so embarrassed now, and I'm anxious and nervous that things won't work.

What happened to my account now?

I can use other services, but I wonder why I can't use only in-app payment.

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I have 15 dollars in my account right now, so please help me to use it.