Hi everyone, I am new to the forum, but actually used it extensively before installing /e/OS on my S9 two days ago. So I thought it might be useful to others to share my experience here.
I had the same issue as LTR and also the libusb -12 error. For me, it worked after switching from my laptop to a desktop PC, using one of the usb ports at the back of the computer. I used the same cable for all attempts. I immediately saw a difference in the process after changing computers, because there was now a thin progress bar on the download screen on the phone before I was asked to restart into recovery by the easy installer.
Also, as I was unsure about this before and it might be good to know for others who want to use the easy installer with the S9: the installer succeeded to flash the old version of /e/OS (oreo), in spite of having had stock android 10 and the latest updates on the phone before. After installation, I could download the OTA upgrade to version q and it is now working smoothly on the latest version, as far as I can tell.
Many thanks to the developers and everyone who is sharing information in the forum.