I purchased a crashed S900 and had to replace various parts including the lower main board.  Is the serial number listed on the small label on the topside of the lower board with the QR code next to it?

Finally have it up and running using a FrSky Taranis Plus and X8R receiver using S-Bus (16 channel mode) attached to the A2.  I don't have the Z15 or GH4 mounted yet, but it is very stable hovering with the gear down at the moment using DJI forums suggested gains.  Have not been willing to do more with it since I need to register it and I'm not sure if that number is the serial number or not to be used to register it.  I have a 520 mm competitor drone that came with its own transmitter, so this was my first radio controlled product where I had to bind and configure a transmitter and receiver to make it work.  I just purchased a DJI Ground Station to install as well.  It's been a little challenging, but I got it bound and configured in a couple hours, now I want to get it registered and out flying and taking video..

OK found the answer listed a little lower in this forum section.  It is indeed what I expected it to be.  I was looking in the PRO forums section, just needed to find the right forum.  Now I can get it registered.  Also just received the DJI Ground Station so will install it in the next day or so and use my iPAD Mini to run it.