How can a student ask for help from another student?

I have created some projects for students to work on and submit.
However, they can only mention (with a @) me and not their teammates; how can that be done?
Is there any way for a student to call a friend to look at their code and help them?

You could invite them to the repl!

There’s no invite when it’s a submission project - at least, I couldn’t find the invite button on the top right…