Is the transaction of buying and selling cryptocurrencies—in which the amount is debited from the account immediately, while the purchased currency is received in the wallet with a delay that may reach 15 minutes—considered permissible or impermissible?

For the validity of trading monetary and electronic currencies, immediate possession (al-taqabud) in the same session (al-majlis) is a condition, based on the hadith (definition) of Ubadah ibn al-Samit (may Allah be pleased with him). If the currency's entry into your account is delayed by 15 minutes, but you have not left the contracting session, this does not cause harm. However, if the session has concluded, a slight, unintended delay that is beyond the control of the contracting parties is excused. It is permissible to dispose of the currency after confirming its arrival in the wallet.