Apple ID in App Store

Click here --> https://support.apple.com/choose-country-region/media-services Select your country, then a product. If you don't see one that handles your issue then keep experimenting with selections until you reach one that gets you a chat session or a telephone call and get the representative to redirect you.

or:

Contact Apple for support and service --> "See a list of Apple phone numbers around the world."

Click here --> https://support.apple.com/HT201232

If you quote specific error messages then sometimes there are specific links for those messages. Yours was pretty general so all I could provide was a general link.

Do you mean a "Your purchase could not be completed" message?

Do as it directs, go to the URL and follow the instructions:

www.apple.com/support/itunes/ww/ --> https://support.apple.com/country-selector/itunes > select your country > Contact Support > Contact iTunes Store Support > Purchases, Billing & Redemption

I also provided a telephone number source.

I always feel so good inside when people say how much they appreciate my volunteer effort on this web site. You do realize that the people posting here are users like you and not Apple (see the fine print at the bottom of the page).