Is the amount of money that the questioner demanded from his relative, in exchange for purchasing a 1980 Toyota saloon car in 2001, considered a debt that he is obligated to pay?

Stipulating an increase in debt is usury (riba), and the procrastination of the rich is injustice. The contract between you two is a contract of agency for a fee. What you agreed upon as a fee is obligatory for your relative to pay. If he is in hardship, he must be given respite, and if he is well-off, it is not permissible to delay payment from him. It is not permissible for you to sell the house without his permission in exchange for your debt unless his procrastination is proven. Your action of purchasing the land is contingent upon the principal's approval, and it has become his property with his consent. You are entitled to a fair wage (ajr al-mithl) for your construction work due to the absence of an agreed-upon wage. You must show him what you spent and what you accomplished, and it is not permissible to add the wages of others. Your claim for the car amount depends on the agreement; if it was for a specific car, you are entitled to its value, and if it was for a specific sum, you are entitled to that sum. You must explain to him that the amount spent for supervision, follow-up, and brokerage was taken by you in exchange for performing these tasks. If he agrees, it is permissible for you to take it; if he does not agree, you are entitled to a fair wage (ajr al-mithl).