Hi, @banpei.lim. Welcome to the SmartThings Community!
Can you check the result of this SSL test by entering the URL you used (https://smartapp1.onrender.com/), please?
Mmm it’s weird, generally, when SmartThings doesn’t accept an URL due to it’s certificate, the site doesn’t pass the test and the confirmationURL isn’t received either. So, we will have to report the issue, for this I need the following:
Details about the issue, I mean the steps you follow and what you see in the Dev Workspace. For example:
I register the app and get the confirmation URL which I copy into the browser and shows the redirectURI registered correctly but in the Developer Workspace I still see the “verify app” button and when I click again on it, it sends a new confirmationURL.
The last part is important because it happens that after the verification, the Workspace might still show the “verify app” button but if you click on it and was verified successfully, the yellow box disappears.
2. Share the App ID that appears in the Developer Workspace.
3. Try to verify it again, take note of the time and share it with us including the time zone. For example: 09:30 GMT-6