When I am on the payment and shipping screen on my phone, the "add payment method" is not highlighted and will not let me click on it to add a payment method. What do I need to do?

Hi, and welcome to the Apple (user-to-user) Community!

Re: "I cannot add a payment method, therefore I cannot buy apps, books, etc on my phone"

As we are all Apple users, like yourself, in the community, we have no access to your accounts or details to check this out for you. We have little info, to go on ... we'd like to help, however:

Your Apple ID is the account you use to access Apple services like the App Store, Apple Music, iCloud, iMessage, FaceTime, and more. It includes the email address and password you use to sign in as well as the contact, payment, and security details you use across Apple services.

You may want to check you are signed in (to your iPhone) with your Apple ID:

Sign in with your Apple ID - Apple Support

If you wish, you can check if any restrictions are set:

Manage App Store purchases, settings, and restrictions on iPhone - Apple Support

If you have disputed a charge from Apple, you may need to authorise your financial institution / card-provider to allow payments to Apple again.

Similarly, International payments may be needing your authorisation.

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Apple support has articles online that may help with adding a payment method etc. If you have active subscriptions or such, you may need to add a new payment method before you can delete an old one.

How to add an Apple ID payment method:

Add a payment method to your Apple ID - Apple Support

How to delete an Apple ID payment method:

Remove a payment method from your Apple ID - Apple Support

How to change an Apple ID payment method:

If you need to change or update your Apple ID payment method - Apple Support

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You can also log-in to your account online, and check or edit your details there:

Apple ID sign-in : https://appleid.apple.com

if needed: How to: Get a verification code and sign in with two-factor authentication - Apple Support

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Trouble-shooting if necessary:

To check which payment methods Apple can accept in your country or region:

Payment methods that you can use with your Apple ID - Apple Support

What to do: If your payment method is declined in the App Store or iTunes Store - Apple Support

or

If a message says 'billing problem with previous purchase' or 'verification required' - Apple Support

If you can’t download or update apps - Apple Support

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If help is still needed:

You may want to reach out to the App Store Support Team, or to "Billing and Subscriptions Support":

(There is a "Get Support" link (or use the support app) at the bottom of their webpages (links below)

App Store - Official Apple Support

or

Subscriptions and Billing - Official Apple Support

All the best :-)