(一):My treat!

我请客!

My treat!
我请客!
Thanks.
多谢。
I'll treat you!

I'll treat.

I'll pay.

(二):Charge it to my bill.

请记在我的账上。

Please charge it to my bill.
请记在我的账上。
OK.
好的。
Please chalk it up.

Please charge these bills to my account.

Please put it on my tab / bill.