None of these solutions work. We have to send them to the Cart or Checkout from Merchant Center. I tried the url/cart/{id}:1 and the domain}/cart/{variant ID}:{quantity}.
Whereas just using the domain/cart or /checkout work fine when testing the link but is unacceptable for Merchant Center
if i leave off the 1 the link works just using {id} but it 404’s when you test the link. Merchant Center is asking for a link for customers to go to the cart or checkout and must include {id} And adding variants and quantity was not acceptable either.