Renting and the "promesse de location"

Hello

New member here, with an urgent question so I hope you don't mind my not going through the introduction thread.

I'm moving to Brussels in a month and after a few visits have finally found a house I want to rent. The letting agent has sent me a 'promesse de location', which indicates the amount of the monthly rent, type of lease and deposit amount. All of those are as he'd promised.

However, he wants me to pay half the first month's rent now, at which point he will send me the lease contract to read. I then have an appointment at his office next week to sign the contract with the owner. I will pay the other half of the first month's rent at that appointment.

The problem is my future employer has advised me not to pay this amount, certainly before reading the lease. The 'promesse' expressly states that it is an advance on the first month's rent, that I will get the money back if the owner changes his mind for any reason, and that I will not get it back if I do not sign the lease by the date indicated (which is after the appointment date, so I'm not worried about that).

The whole principle of handing money over before reading the lease is worrying me. Does anyone have any advice?

Thanks in advance.