AX 2012 Modern POS error: "Device Activiation Error Application Error"

I restarted an old Azure instance of the Modern POS (mPOS) that was once working, and when it was loaded back up, the mPOS loaded up like it had not yet been activated. I'd actually activated it and used the install setup for this instance in a previous post: Retail Modern POS (mPOS) installation and setup via AX 2012 R3 CU8 demo machine.

When attempting to reactivate it, I was getting the error 'Device Activation Error' with the detail 'Application error' (Figure 1 below).

Figure 1 - MPOS activation error: 'Device Activation Errror: Application error"'

I used the normal debugging techniques to try to figure out the issue (Event viewer and Fiddler primarily) to no avail. I also pushed all of the data from AX down to the retail channel again to make sure nothing was out of sync. Note: when using Fiddler, make sure there is a Win8 Loopback Exemption for the MPOS (Fiddler>Tools>'Win8 Loopback Exemptions>'Microsoft Dynamics Retail Modern POS application' [AS OF 9/24/2015]).

After digging more and more, I found out that a setting had been changed in AX for the channel profile of the store where the Retail server URL was reaching out to an Azure address rather than the localhost I was specifying on the Service URL for the Device Activation screen from Figure 1 above. The setup for the wrong setting is in Figure 2 below. The correct setting is in Figure 3 below as well as where you can validate what channel profile the store is using.

The setup in Figure 2 was not necessarily wrong but the setup was not complete hence the error. So I changed it back to what was working locally. To note, the MPOS was installed locally on the same instance as the AX instance. 

Hope this helps!

Figure 2 - The non-working configuration for the retail server channel

Figure 3 - The working configuration for the mPOS. This resolved the error