Hi friends... My theory...
I think...parth used to go to that hotel or resort...
And he would have promised to do a promotional ad for them for some discount..lol... Keeping that in mind, he booked this trip for eri bday... So that he can say it's a promotional trip easily but the hotel people would have a misconception that eri is his friend or someone from his team or gang that spilled the beans...
They know Who eri is. They even decorated her room next day with complementary cake with that sweet note, which eri shared on story.
I think it's parth paid trip. So they thanked him. How they can thank eri when it is paid by parth?