I hold the UK Amex Platinum credit card and one of the benefits is travel insurance for my parents who both have supplementary cards.

I am looking to book them a flight from UK to US (where I reside), I wanted to make sure they have full cover. It has been a while since i looked at the benefits and this may have changed due to COVID. Can I pay on any credit card for their flights or do I need to pay on the Primary Platinum card on this account or one of their Supplementary cards to get the full benefits.