Is it Islamically permissible to engage in agencies that deposit a sum of 300,0 dirhams into the account of someone wishing to establish a company in exchange for 5,0 dirhams, and then withdraw the amount after the deposit certificate is issued, and is this considered lending money with a prohibited increase, and is it permissible for me to mediate between the two parties?

The work of agencies that deposit money into the account of someone who wants to establish a company is forbidden usury (riba) because it is a loan with an increase, and every increase on a loan is forbidden usury. Ibn Abd al-Barr said: "Muslims have unanimously agreed, narrated from their Prophet, peace and blessings be upon him, that stipulating an increase in a loan is usury, even if it were a handful of fodder, as Ibn Mas'ud said, or a single grain." This transaction also involves deception and fraud, and the Prophet, peace and blessings be upon him, said: "Whoever deceives is not one of us." Therefore, it is not permissible to be an intermediary in this transaction due to the generality of Allah's saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression."