Need proof of fund. Please advice

I am a realtor from Jamaica, queens New York.
I have properties that’s selling for 40 cent on the dollar, I need a proof of fund letter to submit my offer ASAP before I loose the deals. Can anyone give an advice as how to go forward. I know the market but I was never involve in purchasing an investment properties.
Thanks for your help.

Also, we put cash into your branch bank for you not a paper POF. This will help you with your bank too.

who does this? are they a lender?