I had the same issue.
To resolve I did the following. Hope it helps somebody else ;)
Firstly, it is necessary to grant the app permissions.
Go to Settings > Apps > OCS-NG Agent > Permissions > Allow Camera / Phone / Storage
If this fails try the following :
1. Clear cache partition on your device *
2. Reboot the phone.
3. Clear data of the app. Go to Settings > Apps > OCS-NG Agent > Storage > Clear data
4. If still did not work, re-install the app then test.
To complete Step 1 (Clear cache partition) *
1. With the phone powered off, press and hold the Volume Down button and the Power button at the same time until the device turns on.
2. Press the Volume Down button until the flag next to the power button reads "Recovery mode"
3. Press the Power button to restart into Recovery mode.
You'll see an image of an Android robot with the words "No Command"
4. Holding the Power button, tap Volume Up once and then release the Power button.
5. Use the volume buttons to scroll to "wipe cache partition" and press the Power button to select it.
6. Use volume down to scroll to YES and power to confirm.
7. At the bottom of the screen, you will see your device go through the process. Once it says "Cache Wipe Complete" the reboot system now option will appear at the top.
8. Press the power button to confirm the reboot.
Note: Clearing the cache may take up to 5-10 minutes depending on user memory.