Pay Apple the money you owe and you can then download and update apps again. If you also use iCloud+ for extra storage then it will let you modify your content in iCloud. Until you do you cannot update or download Store items, nor add anything more to your iCloud storage. You should, however, still be able to download items from there.
Read the links below about various ways to pay for items in the iTunes and App Stores.
- Add a payment method to your account. See this article about payment methods that you can use with your Apple Account --> https://support.apple.com/HT202631 then see this article about how to add a payment method to your Apple Account --> https://support.apple.com/HT201266
- You can use the previous added payment type to go one step farther by optionally using it to irreversibly add funds to an Apple Account balance instead of having the card charged each time.
Click here --> https://support.apple.com/HT208687
If no option is shown to "Add Money to Account" using this method (you only see using gift cards) then it may not be available in your country. Use a gift card instead.
- This article outlines how to redeem an Apple Gift Card or App Store & iTunes gift card --> https://support.apple.com/HT201209
- You could also look into joining a Family Sharing group where the family Organizer's payment method is used. To learn how to join a Family Sharing group, read the section "Join a family group" in this support article --> https://support.apple.com/108380#join
If you fail to pay, Apple does not specify a deadline but keep this in mind:
https://www.apple.com/legal/internet-services/icloud/en/terms.html
VII. B.
"Apple may at any time, under certain circumstances and without prior notice, immediately terminate or suspend all or a portion of your Account and/or access to the Service. Cause for such termination shall include […] (g) failure to pay any fees owed by you in relation to the Service, provided that in the case of non-material breach, Apple will be permitted to terminate only after giving you 30 days’ notice and only if you have not cured the breach within such 30-day period."