"It's a deal!"

Here is a context:

- Thanks for lunch. It was delicious.
- It's OK.
- Next time lunch is on me.
- Don't be silly.
- I'm serious.
- All right. Next time you'll treat.
- It's a deal!

Can you give me other examples of situations this phrase can be used in.
Better more than couple.

Thanks in advance.

It's a friendly way of saying, "Okay, that's what we'll do," or "Okay, I accept your offer."

- Do you want to go to the cinema tomorrow?
- I would like to go but I have a lot of work to do.
- But I can help you so you will have a time to go with me.
- Ok, it is a deal!