I know it can be a pain in the rear. I also have had issues and I have found a fix or workaround for a few of them… I would need more info on the OS of the host, (I can only help if windows) I we also need the step by step and a screen shot or full error or issue… I am sorry I can not read your mind on what how you did it, what your steps were (not the guides) What was the image type, where and what OS is the image?
Make sure you loaded the driver on the windows system for the usb ( in less then win 10) . Check again sometimes you do and sometimes you do not have to short the SPI pins, BUT, once you are connected pull the jumper. Check to and make sure you do not use a USB C to USB A(?) it needs to be the cable they sent and it needs to be usb3 so check your port on your host and use the usb3 port.
Hunt : Make a working image on a SD card make sure it boots and is all happy… it only needs to be the boot os not apps are needed, you can go from here after it boots. But do not try to just burn a image you found on the sites to the ecmm unless you know from your past that it is good.
Once you have a working SD card then take that and make an image of it with Win32DiskImager. Then use this image top burn it…