How to write a receipt or bill?

You should write IOUs, not investment funds. In essence, you don't invest, but lend him money and he invests. Because if it is a partnership investment, you also need to bear the responsibility for the loss. IOU (handwritten by the other party)

Due to the business needs of Xx company, the loan is X100,000 yuan, which will be returned before the end of 2020.

Signature (signature of the other party)

Date, year and month

Plus the bank has a transfer record, which can be used as evidence. Besides, your friends don't look like deadbeats.

Hope to adopt!