What is the ruling on taking an insurance fee to guarantee that registered participants in an activity do not withdraw, given their awareness that it is non-refundable in case of withdrawal?

The ruling on this issue is based on the ruling of discretionary financial penalties (ta'zir bil-mal). The four madhhabs (schools of thought) are in agreement on the prohibition of discretionary financial penalties, to the extent that Al-Sawi narrated a consensus on this matter. Furthermore, only the ruler (wali al-amr) or his deputy may implement it.

Alternatively, insurance can be replaced by setting a fee for participation in the activity as a rental payment for the services provided. There would be a rental contract (ijarah (definition)) between you and the participant, and the amount could be returned to those who complete the activity as a reward.