Dear Naijaloadites, Please Help Me. I Feel I Have Just Been Played

Good day to you all, i really need a serious advice on this issue, am Dapson by name i do process UAE (dubai) visa to people legitimately and the way i go about it.
I do have down payment before commencement and when the visa is out within 4 – 12 days i do send half side of the visa that doesnt contain the visa code.
Couples of months ago, i got a client from abuja troubling me about getting the visa for him and he doesnt mind paying the sum of 400k when the visa is out, claiming he has experience being scammed before, saying he wont pay a dime till the visa is out.
It got to a time, a week ago i told him if am to consider this he will have to sign an undertaking, and we agreed, i sent my friend to him at abuja and we did all that.
Now his visa is out i sent him half copy of it and his insisting on seeing the full, where as he hasnt pay a dime, i dont know what could happen if he sees it, nd his delaying the payment.
If he had paid i will send the full for him so he verify but scared if he sees it and he never attend to me again concerning the pay, and i did this out of favor.
I need ur candid advice on this Naijatwisters.
I Will Be In The Comments Section

Dear readers, after reading the Content please ask for advice and to provide constructive feedback Please Write Relevant Comment with Polite Language.Your comments inspired me to continue blogging. Your opinion much more valuable to me. Thank you.