What do you mean by sending slippers?

Shoes and "evil" are homophonic, so sending shoes is also sending evil, which means bad.

Asia

Slippers are also deeply related to the culture of some specific areas. In many Asian countries, indoor slippers must be changed when entering the house. There are also special bathroom slippers in the toilet, and the slippers of the host and guests are usually different.

tropical zone

It is quite common to wear slippers outdoors in tropical countries. Many people who work on the street have to wear a pair of slippers to work, and most restaurants will not ban slippers.

Tourist attraction

Tourists wearing slippers are also common in some coastal tourist attractions, so some high-end restaurants, clothing stores or department stores will put up "No Slippers" signs on their doors.