Hi ,
Welcome to the Apple Community.
(We are all Apple users, like yourself.)
Sorry you find Apple's system is confusing, and have been experiencing such difficulties.
Re: whats the point!!
Seems it may be just a matter of first getting familiar with the way Apple works.
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Re: "it will not let me use my store currency to buy (Apple Music subscription)
"it’s probably because where i live is the problem"
To check if your 20 dollars is available to use: Check your gift card balance
Learn if you can buy apps, movies, music, books and more,
or use Apple Podcasts or Apple News, in your country or region.
Availability of Apple Media Services – Apple Support
If your card works with your Apple ID:
What you can buy with your Apple Gift Card or Apple Account balance – Apple Support
(NB: Some purchases might require that you have a credit card on file,
even if you use your Apple Account balance to make the purchase.)
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Re: "have tried putting in a visa and mastercard information but they will not work"
Your Apple ID is the account you use to access Apple services,
like the App Store, Apple Music, iCloud, iMessage, FaceTime, and more.
See the article below for what payment methods you can use in your country or region:
Payment methods that you can use with your Apple ID – Apple Support
How to:
Change, add, or remove Apple ID payment methods - Apple Support
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Re: i want to buy a apple music subscription with the money
Music - Official Apple Support Website
Hope this helps you complete what you set out to do :-)