my apple id is different from my purchases one. how do i change that?

You have 2 different Apple IDs and Apple IDs can't be merged. You can try setting up Family Sharing between the IDs if you want to be able to share purchases made with the IDs.

Family Sharing.         

Family Sharing - Set up.       

dezbozan Said:

"how to change my purchases and media email to the one that’s on my apple id?"

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Accounts Cannot be Merged:

This is not an option. As of this reply, Apple Accounts cannot be merged. This all has to do with licensing between Apple and the Studio. So, just stick with the same Apple ID.

Provide Apple Feedback:

Being not an option, provide Apple with some feedback. Let them know your feedback about allowing for the merging accounts. Being there is no direct link for "Apple ID" feedback, perform as instructed here: Apple ID: How to Provide Apple Feedback for this Category

You need to understand that what you call your "media and purchase email" actually is an Apple ID.

What you can do is to delete the what you call "your" (or the other) Apple ID - it would work if you made no purchases with it. That way, you can get rid of that and then use the Apple ID which you have been using for purchases as your only Apple ID.

https://support.apple.com/en-us/HT208501

I have the same problem. Four hours later I cannot change my media and purchase email to match my apple id. Who has an answer please?