The paper for the printer says, “Image this side first” and has an arrow pointing down. Does this mean to put the paper in the printer such that if it were still wrapped up, the arrow on the wrapper would be pointing down? Or does it mean you have to know whether your printer flips the paper over or not and if it doesn’t then you put the paper in the other way? But if it does, you do? Gertrude Stein.
The easiest way to check is get a plain sheet of paper and mark and “X” on the side facing up and send it through…then you can see what side it prints on.
From there, you will be able to tell which way to put the paper in so it prints on the correct side.
Some time ago paper manufacturers realised that people normally only print on one side of the page so they started to finish the paper properly on only one side - this side is supposed to get the toner so you DO have to know if the printer flips the paper over.
I’ve never seen any difference in reality and I’ve experience of a printer that was almost always filled correctly (because I was the only one who did it) and others that were presumably 50/50 - over literally hundreds of thousands of pages.