Answer:
The foot-in-the-door persuasion technique.
Step-by-step explanation:
Also known as FITD, the foot-in-the-door technique is a tactic of persuasion particularly used to make someone agree to a solicitation when they probably would not agree if they were asked right away. The principle is derived from the idea that if a answerer will consent with an small request, so they will after be more likely to agree to a bigger and more significant request .
This technique makes more demanding requests with time, like in the example, it makes the subject feels bound to honor and therefore donate.