This following thread is exactly what you need: Samsung S6 Lite: problem with installation
What I know when flashing Samsung phones with /e/OS is that, after uploading the recovery, you have to press some buttons fast as to avoid booting into the normal Android version again instead of the recovery of the custom ROM. In the video it is referred to as ‘the tricky part’. I didn´t read the thread, but that can be the problem users are facing here.