How to buy expansion pack as a gift?

@annOnymous42  The EA App doesn't support gifting at this time.  (Origin still does, so if you and this person both have at least temporary access to a Mac, that would be a simple workaround.)  But what you can do is buy someone an EA Wallet card, which they can add to their account and use for their purchase.  You can also buy a third-party code for the expansion, but in that case, please make sure you're buying from a trusted retailer:

https://help.ea.com/en-us/help/faq/where-to-buy-ea-games-v2/

Third-party codes don't always work, and EA doesn't provide support for purchases from unauthorized sellers.

The simplest solution might be to sign into the other person's account and use your credit card details, or PayPal, to make the purchase.