Can't invite my friend as an ally while on a server?

[Kubzyy]

Today, my friend and I tried multiplayer for the first time. I'm not able to host my own server so we joined an empty one. In the chat box it said I could invite someone as an ally to share quests and disable friendly-fire. The command said it was /invite <pid>. I typed his name into the command but it just kept saying "Please specify player ID" or something like that. I'm a little confused because in the chat window, my friend's name was showing up as "PolarKhajiit (1)" but the username above his model just said "PolarKhajiit" My username was also showing a (0) next to my name in the chat and I'm not sure why. I tried a bunch of variations like

/invite PolarKhajiit
/invite PolarKhajiit (1)
/invite <PolarKhajiit>

But none of them worked. What is the correct way to type the command so we can actually co-op together? Sorry if this is a dumb question but we couldn't figure it out.

Lastly, if we successfully invite each other as allies, do quests get completed for both of us? Do we both get a share of the rewards? Please let me know. Thanks.

[testman]

the ID is just the number
so you would do just /invite 1