Is it permissible to trade in the product "nicotine pouches" which helps in quitting smoking, and which some bodies have issued a fatwa permitting its use because it does not cause diseases like cancer, but may cause addiction? And what should I do with the money I earned from this trade if it turns out to be impermissible, given that I do not know the exact amount of profit?

Since nicotine is addictive and harmful to health, the default ruling is that trading in it is forbidden, unless there are types that are not addictive and do not cause significant harm to health. Therefore, the questioner must refrain from trading in nicotine pouches, even if there is a 1% doubt. As for the money previously earned from this trade, he is not required to dispose of it, because he acquired it believing it to be permissible, by analogy with money earned from usury, as stated in the verse: "So whoever receives an admonition from his Lord and desists, he may have what has passed, and his affair is with Allah." He also did so relying on a fatwa permitting it, and the layperson who imitates (a scholar) has the madhhab of his mufti. The sin of issuing a fatwa without knowledge falls upon the mufti, not upon the layperson who imitated.