There are several reasons why a local upload might not work. Here are the common reasons:
1. The project location / filename has not been entered correctly in the settings app of your device.
The location must exactly match what appears on the PC screen when you press F5 (and that upload screen must remain there whilst you attempt the upload). Often users miss out the "http://" at the beginning, or use commas instead of full stops for the IP address etc. All the settings are case sensitive. A sample project location will look like this:
http://192.168.1.50:51001
with the "192.168.1.50" being the IP address of your PC. If this address comes up as 127.0.0.1 or 169.254.x.x then you are not connected to the network properly.
If you are scanning a QR code from the PC software, then this information should already be entered correctly.
2. The PC and iOS/Android device are on different virtual networks
This is common when using a Mac Windows emulator where the network is not bridged - you will notice that the PC IP address is not similar (within the same subnet, usually the first 3 numbers are the same) to the iOS device IP address.
3. A firewall / anti-virus program is preventing the upload on port 51001.
This is common - recommend temporarily disabling the firewall / anti-virus program to perform the upload, and once confirmed that this is the problem, configure the firewall to allow communication.
4. The PC is not hard wired to the network
Whilst wireless-wireless uploads usually work, some wireless routers prevent it - having your PC hard wired to the network, with Wifi turned off may resolve.
5. The upload screen is closed down on the PC
When you press F5 / Upload to device, you need that upload window to stay open whilst you attempt the download - do not close it down
6. Incorrect password entered
If you are uploading to Android, the project must be locked from the project tab. If the project is locked, the same password must be entered on the iOS/Android device in order to load the project