How do i transfer the money from my app store balance to my apple pay.

It is not possible, you need to contact Apple Support to request a refund, see -> Check your Apple ID balance -> Check your Apple ID balance – Apple Support (UK)

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If you have Apple ID balance you can't use.

You can't redeem or return Apple Gift Cards, App Store & iTunes Gift Cards or unused Apple ID balance for cash, except as required by law. If your jurisdiction allows the refund of redeemed gift balances, you can contact Apple Support to request a refund. 

When you contact Apple, include the following information:

•               Your Apple ID.

•               The refund amount.

•               Your current delivery address.