I've been reading that you can only use data from one SIM at a time. If that is in fact the case, if the SIM your trying to use for GM doesn't have data, they wont work.
Switched so that it uses data from sim 2, still no group messaging when the others are using iMessage. If someone using message sends me a single message, it shows as sent as text, so it knows I don't have an iPhone. The problem lies in group for some reason