I am developing gmail contextual gadgets using my personal gmail account. I am using sample "hello world" example code listed on the google documentation page. In my project I have enabled "Universal navigation extension" and "gmasil contextual gadget extension". Top navigation menu shows up properly for my app but gmail gadget is not working. Here are the few of settings I have tried
Am I missing anything that I need to enable for testing my gadget with gmail.com account.
This is not supported -> you need a paid account.
You might also want to consider whether you want to go down this path - as there are now Gmail Addons set to be released later this year.
https://gsuite.google.com/campaigns/index__gmailadd-ons.html
Gadgets are on the way out I would expect - no enhancement to gadgets for years.