*** This Printer has 4 different Paper feeds: main, photo, rear and manual. The system settings also allow to select "automatic". The printer settings can also be set in Okular. But Okular does not care of the settings. It always takes the paper from the feed "main". Only when "automatic" is selected in the System settings, Okular takes the paper out of the "rear"-feed whwn selected in Okular settings.
If you want to use the rear paper feed of the Epson ET-8550 with Okular, you need to make the following settings in the printer drivers: In System Preferences / Printer / Printer Setup: Media Source: Automatic In Okular / File - Print / Properties / Advanced / Media Source: Rear If one of the two settings is incorrect, Okular will use the main feed, i.e., the paper tray below the printer. Another point is printing pages containing QR-code. The job is visible in the queue for a few seconds, then it disappears, but nothing comes out of the printer. It is possible to print such a page using "lp" on the command line. The soution is: You have to make following setting in Okular: Print / Settings / PDF Options / Force Rasterization = YES With this setting, Okular prints pages containing QR-codes. With this setting, Okular also uses the rear paper feed, regardless of the system settings. Unfortunately, Okular forgets the setting from job to job, so you have to navigate through the cumbersome menu every time. Luckily, there's also LibreOffice – you can also print PDFs with it. No problems at all.