Just started having this issue today, where trying to use the iOS companion (0.9.12) I encounter the following problem:
It just hangs here, never throwing an error and never displaying the app on my phone (running iOS 14.5 beta 2). I've tried with multiple projects, and all of them hang on sending the final asset.
Can anyone else reproduce this issue?
It might be that your App Inventor session is stale. Do you still see this if you reload and try reconnecting?
Also, double check that you are using App Inventor over HTTP and not HTTPS, as the iOS version doesn't yet support the newer WebRTC connection model that is required for HTTPS.
App Inventor session is definitely fresh, I logged out and back in a couple times before posting to make sure that wasn't the issue. Also using AI over HTTP simply because I didn't realize HTTPS was implemented yet 
One thing I've yet to do is try over a different network—I'm on my school network where nothing AI2-related should be blocked, hasn't been for years—simply because I don't have another one available at the second. My impression is that a cellular connection shouldn't work, but I tried it anyway and am actually encountering the same issue.
Yes, your computer needs to be able to make HTTP calls on port 8001 to the iOS device. Cellular connection won't work until WebRTC is implemented.
As a data point, I just tested on my home network with Hello Purr and the assets loaded correctly. You may want to check with your school IT that they didn't change any firewall rules over the weekend.
Will do. Weird thing is that it only happens with my phone running iOS — the Android tablets we have here for this exact reason work just fine connecting from my computer.
Do the Android tablets work if you check the legacy box?
I'll have to try once I'm back, out of the tech room for today. I'll try it on my home network with a couple devices and see what the outcome is.
Please teach me why pop up that error ??? ; Error from Companion: error: Unable to activate constraint with anchors and because they have no common ancestor. Does the constraint or its anchors reference items in different view hierarchies? That's illegal..
This sometimes happens when you have an invisible table arrangement or one of its children is invisible. If you send us the AIA we can inspect further.
I have this issue to. It will stop at 98% while loading mp3 files.
But it only happens on my IOS device, the android tablets work completely fine.
The iOS companion works in the same mode as what the Android companion calls Legacy Mode. This requires that the computer can reach the phone or tablet on its local IP address (as shown on the main screen) on TCP port 8004. This is easiest if both devices are both on the same Wifi network (such as a home router). If you're in a school environment, you may need to have your network administrator ensure that the network is configured to allow the two devices to communicate with one another in this way.
This is happening to me as well. It gets to 98%. I uninstalled the Companion on my phone and reinstalled and I get an error.
Now I only get an error that says: Companion Connection Error. See help page. The help page has nothing about the Companion. I am using iPhone 13 and have Companion Version 2.60 (build 8) installed.
