Added to a teams chat, but the chat isn't appearing anywhere

I was added to a group chat from a third party vendor (someone outside of my organization) and I am getting the emails sent to me that say "Dianne sent a message to your group", but the actual chat never appears for me to look at what people are saying or to respond. I can't get it to show up on the desktop app, cell phone app, or browser version.

I have other chats that I can see and respond to, but not this one.

Any suggestions on how to get this chat to appear?