Open the game in the Just Play app, find the invite option in the team lineup section, copy the share link and send it to whoever you want to play with. They open the link, land on the same game, and book their own spot.
Step by step
Open the Just Play app and go to an upcoming game
Scroll down to the team lineup
Select the invite option and copy the link
Send it by message, email, or however you normally reach them
The link points at that exact game, so your friend does not have to search the listings or work out which venue and time you meant. Send it early rather than the day before, because spots are limited and the good games sell out.
Will we be on the same team?
You will be in the same game. Whether you end up on the same side within it depends on how the numbers land on the night, and that usually gets sorted out when everyone arrives. If you want to be on the same team as a mate every week for a whole season, that is a different thing and we guarantee it: see Can I play with a friend, or sign up as a group?.
Who pays
Your friend books and pays for their own spot. You can't pay for someone else's booking.
Bringing someone to a season game instead
If you play a season and want a mate to cover you for a week, that is a substitution rather than an invite and it works differently: see Substitutions: how do subs work, and can I bring a fill-in?.
Still need a hand? Find a game worth inviting someone to, or read What is One Game? for how One Game works.