flight ceiling removal

I need to fly in a BLUE restricted zone, which has a max ceiling of 0 feet due to relative proximity to an airport. I understand I am required to perform 'custom unlock'. However, using the Kittyhawk app to custom unlock, I set the maximum height to 50ft but get the message 'Pre-Check Failed'...

I have been flying my Mavic for about a year now and have modded and tested a bunch of different antennas and recently just stepped up to the Command Case from Titan Drones. If anyone has questions about mods on the Mavic (software/hardware) shoot me a PM and I'd be glad to answer any questions...