#!/bin/sh

loggedInUser=$(/bin/ls -l /dev/console | /usr/bin/awk '{ print $3 }')

dseditgroup -o edit -d $loggedInUser -t user admin

Give it a shot

It's also possible the admin user is the only administrator account on the machine that has a FileVault securetoken.  macOS restricts you from deleting that user even if there's some other mechanism to hand out securetokens to users like a valid bootstrap token being stored in the MDM server or Jamf Connect installed to make more user accounts.

You'd need to elevate another user temporarily to an admin account, delete the user, and then demote the temporary admin...

unfortunately it does not work 

the macs has another admin account which is why i want to revoke the other one (the current login user). 

i manage to found this command  but i cant do a whitelist of the admin account according to the username since different set of macs have different admin username

I tried it on a test machine and it works !! what does it say in the logs of that policy?

i recreate back the script & policy and it works now. thank you