Is it permissible to give money from Zakat to a relative who is eligible for Zakat, with the intention of it being Zakat, in the form of a loan contract with guarantees, so that he may invest it in a project such as a grocery store, and then the money is paid to him after the repayment of the loan for another purpose, such as marriage, due to his previous mismanagement of money?

Zakat must be given to those who are deserving without giving them the impression that it is a loan, as that involves lying and causes distress to the debtor. If there is a fear of squandering the money, then it is permissible to purchase the needs of the poor with zakat. It is preferable that this be done with their authorization, such as asking the poor about their needs and then purchasing them for them. If authorization is not feasible, then it is permissible to purchase what they need without authorization, acting upon the opinion of those who permit giving the monetary value when there is a need or benefit, which is the choice of Shaykh al-Islam Ibn Taymiyyah and was Fatwa by Shaykh Abdul Aziz bin Baz.