We are currently working for online food order system. This is how our site looks like
When user select an item from menu for the first time it asks user for address and validate whether it can be deliverable or not. Now we want to ask user whether he want to add some tips. Currently we are thinking of two options
Show a pop up when user clicks order and ask him whether he wants to add some tips or not.
Move it the next page when user enter his payment information.
I am wondering which one from the above two would be the better approach. Or if there any other approach we can follow?