If you can't make purchases or update apps, including free apps, you need to update your payment method or add a new one.
You need to have a payment method on file, even if the app you want to download is free
See ⤵️
Payment methods you can use with your Apple ID
Payment methods you can use with your Apple ID – Apple Support (UK)
Add money to your Apple ID balance
Add money to your Apple ID balance – Apple Support (UK)
If you update your payment method or add funds to your Apple ID balance, It would take about 1 to 3 business days in order to process.
If you're still unable to update your payment method, Contact Apple Support.