How do I accept a fireteam invite?

[WoojTheTall]

I'm pretty new to Destiny 2; and when I get a fireteam invite from a friend I click the notification in the corner of my screen and then click "accept invite." But I always get an error message that says my friend must be in orbit or in an activity for me to join his fireteam. This has happened three times in a row now. Am I doing something wrong? Is there another way to accept invites?

[Lil C]-[ew C]-[ew is ☂д☂]

As the message described he as being the leader sending the invitation to join his fireteam. Is he that need to be on orbit so you can join him.

[WoojTheTall]

I forgot to clarify: other people from our clan are joining him but I can't.