James nodded in appreciation as she told him, “Don't worry I want to pay this is just my way of welcoming you to London. So the food is on me. Don't hesitate to order what you want."
James felt he should still do something gentlemanly and polite, especially since he wasn’t the one ordering and paying. But another polite thing to do is to accept when someone is doing something nice for you. It makes them feel better about themselves, which makes it a sort of service to them when you accept their compliments, gestures of generosity, and other polite things they may do or say to you or others.
Soonce the two of them reached the front doors of this completely unfamiliar restaurant (at least to James, it was), James stepped forward and reached to open up the door for Eri. He held it open for her to go in, and was prepared to follow  her inside the restaurant.
“After you, ma’am.” James said playfully and made a grand gesture with his free hand, finishing in a slight bow and an arm pointing her way into the restaurant. He made sure to make it obvious that he was playing around, also hoping to make her laugh a bit.