I have an iPad Pro 9.7" and it's bricked after an ota update to 9.3.2 (error 56). I've seen so many responses now having the same experience, that I conclude that this is something serious and Apple needs to address it.
Apple support can not help you. You either send it in or go to an Apple Store (after making an appointment) to get a "new" iPad to replace the bricked one... untill Apple releases a 9.3.3 update.
What I hate about all of this: you did nothing wrong, your iPad Pro was fine and Apple provided you with an update with security improvements to update. After this update your iPad Pro is bricked. Do they send you a carrier that exchanges your iPad Pro with a working one, since you have Pro product that you use for work on a daily basis... Nope. Send it in and wait a week or take time off and travel to a store... If you provide Pro products, you should provide Pro service standard!
Read about more users here:
https://discussions.apple.com/message/30219004?ac_cid=tw123456#30219004