International Group iMessage

Can an iPhone with an international number be added to a U.S. iMessage group?

I live in Spain and have a Spanish phone number associated with my iPhone. My family in the States has an iMessage group (and all of them have iPhones as well).

When I was in the States, I was part of the group, but since switching my number, I haven’t received any of the group messages. My sister has tried adding my new number but says iMessage won’t allow my Spanish number to be added.

Is there some kind of restriction when it comes to adding an international number to an iMessage group?

My Spanish carrier doesn’t charge for iMessage conversations and I don’t remember that being an issue for iPhones using iMessage in the States either.

Am I missing something? Just want to be a part of the family group chat again. Thanks for any help in advance 🙏🏼