What do I have to do when I am trying to download an app but it says your account has been disabled?

Please check ⤵️

1.

If your Apple ID is locked or disabled -> If your Apple ID is locked or disabled - Apple Support (CA)

-> Get a verification code and sign in with two-factor authentication

Get a verification code and sign in with two-factor authentication - Apple Support

2.

If you see a message that says "Your account has been disabled in the App Store and iTunes", there is a problem with your payment method on your account, to resolve the problem you need help from Apple support,  click -> contact Apple Support for help.

If you have followed all the steps and instructions and if you still need help, get more help and assistant from Apple directly, see Contact Apple for support and service -> Contact Apple for support and service – Apple Support (UK) 

Hello,

If or when you see a message saying "Your account has been disabled in the App Store and iTunes" or "You cannot login because your account has been locked", you must contact Apple for help. This is not something you can fix yourself. Apple provides a chat link for this specific issue. Tap or click here --> https://getsupport.apple.com/?caller=kbase&PGF=PGF63005&category_id=SC0245&symptom_id=23362

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Based on the support article: If a message says 'Your account has been disabled in the App Store and iTunes' - Apple Support

Click here and contact Apple Support when they're open; if the link doesn't have an option for your country, use this form.

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It's clear from your post what the reason for your disabled account is. Niel and I both caught it so just follow the directions in either of our posts.