A note written to the sender as evidence after receiving the money or things handed in is called a receipt. A complete receipt includes title, text, signature and time.
IOU is a kind of documentary application written to the relevant unit or individual when an individual or unit owes money or things. White stripes are also called "IOUs" today. IOU is also a common written document in daily life to prove that one party owes money to the other, and it is an application style of credentials.