Green “join” showing up in some Contacts iMessage thread but not others. What does this mean?

Hello Heeyybree,

Thanks for reaching out to Apple Support Communities. Upon review of your post, it seems that you want to know why you see a green ‘Join’ button on some iMessage contacts. We can see why you’d want this clarified, so let us help from here! That button represents your ability to join a Group FaceTime call. Learn more about this here: Use Group FaceTime on your iPhone, iPad, and iPod touch. Check the “Join a Group FaceTime call” section.

Please let us know if you have follow up questions, so we can continue assisting. Take care!