Unable to add payment method on my iPhone

Hi khushbu275

welcome to the Apple (user-to-user) Community.

Re: "My Iphone 14 plus doesnt allow me to add payment method.

This is greyed out and I'm unable to make any purchases"

You might want to check the payment methods that Apple can accept in your Country or region:

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

Check that you are signed in (to your computer or device) with your Apple ID

Sign in with your Apple ID - Apple Support

Re: "Can some help plz"

Wondering where, (and on what device) you are trying to add the payment method.

If your Apple ID is locked or disabled after entering too many wrong log-in attempts

What to do: If your Apple ID is locked or disabled - Apple Support

or

Your Apple ID is the account you use to access Apple services, like the App Store, Apple Music, iCloud, iMessage, FaceTime, and more. 

You might want to try accessing your Apple ID account online. (You can check everything is in order, up-to-date, and make any changes there).

Apple ID Log-in:

https://appleid.apple.com/

A verification code will generally be sent to a trusted device listed in the account.

Help with verification if needed:  

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

More support if needed:

Apple ID Support Webpage:

Apple ID — Official Apple Support

All the best :-)

Re: is having Apple ID via mobile number an issue here ?

In some countries a mobile number can be used as the username.

Many of us use an eMail address as our Apple ID username.

Apple Support's article: Use your mobile phone number as your Apple ID

says:

" If you create a new Apple ID on an iPhone in iOS 11 or later, you can use your mobile phone number as your user name in China mainland and India. If you live in China mainland, use your (+86) mobile phone number. If you live in India, use your (+91) number. Depending on your carrier, you might also be able to create a new account with a phone number on some Android devices, smart TVs, and streaming devices. Just choose Create Your Apple ID from the Apple ID sign in screen and follow the instructions to create your new account".