Hi Lard, the boot can be loaded through TFTP. When you go to Admin -> File Management -> Upgrade/backup Firmware, you'll notice the boot option is grey when the HTTP/HTTPS is selected. If you choose the TFTP option everything becomes active.
If you don't have a TFTP server, you can download TFTPD32 (332 bit) or TFTPD64 (64 bit). It's free and very basic.
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