Nitro Pro not opening from Sharepoint

[Christian LeNabat]

I have deployed the app (v1.12.0.39) to our Sharepoint tenancy and made it available for all our sites and users.  The "Open with Nitro Pro" button indeed appears on all our sites.

I had a test user ensure his Nitro Pro was updated to 13.67. But when the test user tried to open a PDF with the new button, nothing happened. Test user: Win 10, Chrome browser (set to open PDFs in browser, as opposed to download).

After learning more, I configured the test user's Nitro settings to add two Sharepoint locations - the root document library, and a subfolder within the document library (in case the first location didn't support tunneling to subfolders). I also changed his DMS Storage settings to open files without checking them out, since we don't use this feature in Sharepoint. The test user still cannot open PDFs with the Nitro Pro button in Sharepoint.

The Nitro installation guide advises to match the Sharepoint extension with the Nitro Pro version:

1.0.0.8 - >13.45
1.2.0.x -> 13.46 - 13.48
1.3.0.x -> 13.49+

...except that the only version of the Sharepoint extension offered by Nitro website is 1.12.0.39. Is this discrepancy in extension version where our problems lie? Also, notice that I've also been using Sharepoint "app" and Sharepoint "extension" interchangeably, here. But I can see Sharepoint referring to Nitro as both an "App for Sharepoint" and a "Tenant Wide Extension". Is there a distinction that I should be observing that matters to Nitro-Sharepoint integration? 

Thank you for your help.