What is the ruling on money remaining from a sum taken in exchange for issuing labor visas, part of which was lost and the rest invested in a business project with lawful money, and is self-purification obligatory after the other party has benefited from the transaction?

If the mentioned amount is a fee for your effort in obtaining visas, then it is your property. However, if you do not complete the work, you must return the amount to its owner. But if you were entrusted with the amount to obtain visas for the company, then your disposal of it without permission is a breach of trust, and you must return the amount to the company, unless they agree to take compensation for it.