I am trying to add a american express gift card to my apple account to pay for my icloud. Why does it keep getting declined?

Hi mck1193

Welcome to the Apple Community.

We are all Apple users, like yourself, in this community, and can not speak for Apple, and it's processes.

Seems Apple can not accept all payment methods in all countries.

and not all products from all financial institutions can work with Apple.

You can see which payment methods Apple can accept in your country or region in the article below:

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

All the best :-)

Most such gift cards cannot be added to the wallet