You need to activate your device via iTunes or WiFi.

Learn what to do if your iPhone can’t be activated, an alert says the activation server is unavailable or the SIM card is unsupported. Check the detailed guide here https://support.apple.com/en-us/HT201407

Step 1: Reconnect your device to your computer and launch iActivate tool. Click on Start button.

Step 2: Continue with setup instructions on device using WiFi or cellular connection.

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Method #2   To fix that please put your device in DFU (recovery) mode and restore in iTunes. After restoring set it up as new and go to MDM login screen on the device (follow activation steps from Hello screen to MDM settings). When device will be at MDM login screen open iActivate and repeat the process. If still doesnt work please repeat the whole process a couple of times and it will work.

Some troubleshooting to do before resubmitting the imei for processing.

Must Update to the latest Operating System.

Update the Playstore & Device Unlock App [Latest Version].

Some other Troubleshooting for APP Unlock FAILED message:

1) Try doing a hard reset (memory reset) so the cache of device is clear and also try taking out / swapping sim cards if possible and making sure you are connected to a strong WiFi signal.

2) APP unlock "fail": We found a  fix if anyone else complains of the unlock "failing". It looks like the app remembers the last attempt of the unlock or remembers the last "invalid sim" entered in the phone and will stay in the "failed" response until the app is cleared: 

How to do that?: 

1. settings
2. apps 
3. app manager 
4. look up "device unlock" in app manager 
5. clear cache 
6. also clear data. 
7.exit out.

Now restart device unlock app and the unlock will complete without errors! as always thanks for the support hope this helps future customers problems/questions.

If this still doesnt work, the next step is to reprocess your IMEI.