@Anonymous and others:
There is an issue with your URL: there can not be a trailing slash at the end...
Launch("https://web.powerapps.com/apps/1ae4e9f9-8aaf-46c2-97ff-6038931ea0fe/", "MyUserId", "MyUserId")You can mitigate this by either deleting the trailing slash or by just specifying the app ID with the provider prefix like....
Launch("/providers/Microsoft.PowerApps/apps/1ae4e9f9-8aaf-46c2-97ff-6038931ea0fe", "MyUserId", "MyUserId")
Additionally, when entering generic websites into the launch function, make sure to specify the protocol.
For example, if you would like to open bing.com on your phone's browser, you would need to specify the "https://" at the beginning like:
Launch("https://bing.com", "param1", "param2")
It was still incorrect that you had an error displayed with the address that you used, and we have filed an appropriate bug on it.
I hope this helps and resolves any issues.