Can't respond to group messages

I started a group text message on my iPhone, but now that I'm on my Mac there's no place to respond to the messages. I can still do so from my iPhone, but it's annoying to have to keep switching back and forth.

All the texts and photos, etc., are appearing in the Messages on my Mac, there's just nowhere to add/respond at the bottom.

Anyone else having this issue or know how to fix it?