I can’t download anything

See these can't-download possibilities:

For this one, you will need to use one of the support options below.

'Your account has been disabled in the App Store and iTunes' https://support.apple.com/en-us/HT208856. This link says: "There might be a problem with the payment method that you have on file. When you see the message, don't try to edit any of your account information. Instead, contact Apple Support for help.”

Try using the Apple recommended support link above first. But, this site is down/not fully functional very often. Use the support options I give below if necessary.

You can use Apple Support Twitter https://twitter.com/AppleSupport There may be an hour or so wait.

And, if necessary, go here to contact iTunes worldwide support via text or chat https://support.apple.com/choose-country-region/itunes After choosing your country, see the heading, Tell us how we can help.

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If you can’t download or update apps on your iPhone or other Apple device https://support.apple.com/en-us/HT207165

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If you can't connect to the App Store, iTunes Store, or other Apple services https://support.apple.com/en-us/HT201400. There have been quite a few Apple server connection problems lately. Among other things, in the above document, see Check Apple’s System Status page. You can check there to see if the needed server is available when you need to use one.

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What to do when the Mac App Store shows a different Apple ID for software updates https://www.macworld.com/article/3267709/mac-app-store-apple-id.html. This document refers to a prior owner (use the discussion in it this is your situation), but is also applies to cases where a current owner's old Apple ID is the problem. The discussion below relates to the second possibility. 

Basically, If an app is purchased/downloaded using one Apple ID, then you can't update it with a second Apple ID. The app is inextricably linked to the first Apple ID. You'll have to delete it and purchase/download it again with the second Apple ID unless you set up family sharing (see below).

You can set up family sharing between the IDs to share purchases made with them. See:

Family Sharing  https://support.apple.com/en-us/HT201060

Set up Family Sharing https://support.apple.com/en-us/HT201088

Some other things you can try. Do you have access to another WiFi network where you can try? That has worked for several people.

Try a restart.

Restart your iPhone, iPad, or iPod touch         

Try a forced restart.

Reset Device.      

If necessary

Hard reset.        

Do a backup and try a factory reset. Then restore from your backup.

Restore to Factory setting.      

Backup - Restore your device from an iCloud or iTunes backup.      

See the first possibility I posted above.