We're still ON for dinner next week

A: I’m just here to make sure we’re still “on” for dinner next week. My boyfriend is way too excited to cook for other people.
B: Fig will make a show of pushing food around her plate, and I’ll eat for both of us.
A: Okay.
B: I look forward to it. Thank you.
A: Me, too.

Question: I’d like to know the meaning of “on” in the sentence. How do you use it with this meaning?
Thank you!!!

To be on for an activity means to be ready for it.
It is also means it was planned previously and that person is agreeing to it.
Like if i had a doctors appointment in a week and i ran into my doctor at the supermarket i could say are we on for that appointment? Its very casual so you would have to be cool with your doctor lol.
Another example
Are we still on for hunting?
Oh yeah, im totally on for it i got my permits (for hunting) and all the food i can carry.
(These people previously talked/planned to go hunting together.)