..and the (fixed & unique) IP address of the PC is - - - - - ?
Directly linked or through another device (which also have an IP address)?

Was the HMI configured in the OS configuration to only accept a download when it is placed in download mode?

Hello,

Perhaps you can give some information about the error you have?

Have you seen these links:

How can you transfer a WinCC (TIA Portal) configuration to an operator panel using Ethernet?

And when using TIA Portal v16:

When loading a panel from WinCC (TIA Portal), why do you get the error message "Loading is aborted due to a transfer error: 8020AB001A06FFF4!"?

Best regards,

Wizard