Print diffrent type files with lpr at once

Question

I want to print different files using lpr command to a thermal printer. They need to be printed at once because they're from the same receipt. If I use the following commands

lpr -P POS58 aux.txt

lpr -P POS58 qr.bin

They are printed fine but there's too much time in between the first and second printing. But if I do it like this

lpr -P POS58 aux.txt qr.bin

Only the first file is printed, it doesn't happen with same extension files but it happens here. How could I print all at once?