All perfect praise be to Allah, The Lord of The Worlds, and may His peace and blessings be upon our Prophet Muhammad and upon all of his family and companions.
Contests in which speculations of having financial win or loss are prohibited .i.e. winning the reward or losing the cost of the message as mentioned in the above question, since this is considered gambling which is mentioned in the Holy Quran and Prophetic Sunnah. Besides, scholars considered gambling one of the major sins, for Allah, The Exalted Said (What means): ”O ye who believe! Strong drink and games of chance and idols and divining arrows are only an infamy of Satan’s handiwork. Leave it aside in order that ye may succeed. [5:91] Satan seeketh only to cast among you enmity and hatred by means of strong drink and games of chance, and to turn you from remembrance of Allah and from (His) worship. Will ye then have done ?” [Al-Maidah/90-91].
Therefore, Islamic Sharia prohibits all images of transactions based on gambling whether this was through a contest, game and the like. In addition, the point behind the prohibition of gambling is to preserve people’s assets from manipulation, hindering them from being involved into eating people’s money unjustly and using their assets for the purpose of benefitting the nation through the means of lawful profit. As for the modern images of gambling, they are the worst means of corrupting societies and wasting their wealth. And Allah Knows Best.