How to invoice the calligraphy and painting purchased by the unit? What are the specific requirements for invoicing?

It should be calligraphy "XXXX", Chinese painting "XXXX" or oil painting "XXXX", or calligraphy and painting works "XXXX", unit: piece, fee: XXXX. That's about it. If you want to sell calligraphy and painting works, you still need to find a gallery to open them, because Zhangzi should be a cultural management unit.