What are prepaid response letters?

Question

Marketing

I read here https://spark.ru/startup/rocket-callback/blog/7238...
But I still don’t understand what it is, what it means at all

Answer 1

The answer is here tema.livejournal.com/2354920.html

Answer 2

I don't think any decryption is needed.
These are ordinary paper letters, banks often do this.
They send you a questionnaire / application / card, and the letter contains an envelope with a stamp.
Just made an answer and sent.