I get this message a lot on my Galaxy S8 using Textra. There seems to be an ongoing issue with Verizon and getting group texts on Androids that Verizon doesn't want to fix. There are many, many threads on these boards relating to it, and Verizon customer service people will respond with the same canned messages that do not address the issue at all. I have no idea how to actually get in touch with someone at Verizon who will listen. It's absolutely infuriating, and I would leave Verizon in a heartbeat if there weren't other people on my plan. No one else I know with an Android on other carriers have this problem.