Ruling on buying an account on Amazon that already has a certain amount of credit, in return for more or less than what is already there
Question

Is it permissible to buy an account on Amazon that already has a certain amount of credit, in return for less than that? For example, the account has credit of 1500 dollars, and I am buying it for 400 riyals.
Praise be to Allah.It is not permissible to buy an account that already has credit for cash that is less or more than that amount, because this comes under the heading of riba al-fadl [an exchange of two similar items that differ in quantity], unless the purchase is made with a different currency, such as if the account is in dollars but it is bought with riyals. In that case there is nothing wrong with it, because with the difference between the two currencies it is permissible to have different amounts, but that is on condition that the exchange takes place in the same sitting as that in which the deal is drawn up.
The basic principle regarding that is the report narrated by Muslim (1587) from ‘Ubaadah ibn as-Saamit (may Allah be pleased with him), who said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “Gold for gold, silver for silver, wheat for wheat, barley for barley, dates for dates, salt for salt, like for like, same for same, hand to hand. But if these commodities differ, then sell as you like, as long as it is hand to hand.”
Currencies come under the same rulings as gold and silver.
It says in a statement of the Islamic Fiqh Council:
With regard to rulings on paper currency: it is regarded as legal tender and things may be valued in terms of it in a complete sense; it comes under the Islamic rulings on gold and silver with regard to rulings on riba, zakaah, salam transactions [payment in advance] and all other rulings.
End quote from Majallat al-Majma‘ (issue no. 3, vol. 3, p. 1650).
So it is permissible to buy 1500 dollars for 400 riyals, on condition that the exchange takes place in the same sitting. This is what is meant by the words of the Prophet (blessings and peace of Allah be upon him) in the hadith, “as long as it is hand to hand.”
So you should take from him the details of his account, and give him the riyals in the sitting in which the deal is made, hand to hand. This is an exchange in the real sense. Or you could deposit it in his account in the same sitting in which the deal is done, and this may also be regarded as the exchange by implication.
And Allah knows best.