No need to provide an approval letter.
Just provide the agent a copy of your most recent bank statement. Make sure to cross out the account number.
That should do it. It's quite easy and seems harder than it should be.
I advise my clients to have the proof of funds ready, and I always present it along with the all cash offer.
That way, we have all of our ducks in a row. Maybe your agent forgot, but no harm done since its something that can be remedied within a few hours.
On the other hand, if you do not have your own agent, and have not presented an offer yet; please interview several experienced agents. Then, pick the one that you feel most comfortable working with. A buyer's agent will protect your rights more than someone that works first for the seller.
You can request for help on this forum, or contact me.
Realtor, Certified HAFA Specialist (CHS)
Coldwell Banker Residential