Have you tried this error on MOS.
There are many notes with similar issues, just sharing one such note
Move Order Transaction Transfers More Than Requested Quantity After Error "There must be a valid blanket purchase agreement in effect for the item you wish to transact". (Doc ID 2248159.1)
Thanks for recomendation.
You don't think there is another way to solve this issue?
Sorry, we don't use move order at our site so i don't have enough experience on this.