Is it permissible to give the banker an uncertified check or a promissory note in exchange for transferring currency outside the country without an increase in price and with the consent of both parties?

Currency exchange is considered a currency transaction (sarf), and a condition for sarf is mutual possession (taqabud) or what takes its place at the contracting session, such as a certified check. As for an uncertified check or a trust receipt, they do not take the place of possession, and therefore, it is not permissible to conduct currency exchange with them, even if both parties agree.