Sorry. Running CC2019 all updated. PC Windows 10 64 btit Adobe Extension Manger does not recognize your extension. I have tried manual install, per your instruction, as well, rebooted, etc. but it is not showing up in Extensions.
Try using PVIIexman. One user suggested me that it's the best installer for zxp files. Manual install should work, be careful to follow the steps exactly.
It is already compatible with the latest Photoshop (2021) but when you install it it will be located inside the Window > Extensions (Legacy) > BBTools Shadow. In the future I will make it as a plugin using the latest technology that Adobe supports. Legacy extensions will be there for at least one more year.
If you are using Windows you can install the extension using the Extension Setup Tool (download link is at the end of the message).
Extension Setup Tool is a BatchScript and for some extensions (PostProduction Master and Glow and Glare) you would have to run it as administrator (right-click on the file and select "Run as Administrator").
Before running the script make sure that:
The script (.bat file) is located in the same folder as the extension file (.zxp file)
It's working. Please send me your screenshots and write me directly for faster solutions. It is working because a lot of users that have the latest PS confirmed it, not just me. I can help you solve the problem. My mail: [email protected]