This is helpful.

It is true that buying and selling without exchange may be controversial from a legal perspective, but if the legal controls are met in such transactions, such as a clear agreement between the seller and the buyer, and guaranteeing the rights of both parties, then there is no legal impediment to that. The controls include that there be a valid contract, that there be no fraud or harm, and that the commodity and the amount be known and specified. Therefore, if these controls are met, then there is no harm in such transactions... Therefore, it is better to go back and inquire from trustworthy religious people such as scholars or jurists who specialize in Islamic law to confirm the legal ruling accurately. They have sufficient knowledge to understand the details of matters and clarify the legal controls related to buying and selling without exchange.