Initially, I built up a test agent on DialogFlow console according to the document, and it works well on the Actions On Google which is a simulator of Google Assistant on mobile devices.
Then, I deployed it through the Release in the left menu as you can see the pic attached.
After that, I added some Alpha Testers including my colleague and sent my opt-in link to my colleague, besides, I granted them all the viewer permission in IAM.
However, problem appeared. It didn't work well on my testers’ phone(IOS 10+) but only worked well on developer's account(mine). When they opened the link I sent to them, and clicked send to devices, then clicked the notification on top of the screen.
The result is shown as below.
Google Assistant didn't respond to "Talk to mytest app"
In my case the command was set as "Talk to hello qad", and it did work well on my phone used the developer account.
If my tester input the text "Talk to hello qad", it just replied some direct searching results not hello qad diaglog.
To recap:
My action has already been in "deployed" status for couple of days
I've added the tester accounts in whitelist and give them "Viewer" permission in IAM
Testers could see the action directory page in devices by open opt-in link, but they couldn't see the "I'm In" button and couldn't access the action
Appreciate for any help or advice