Links to the code and device would be nice. The Tx/Rx lines to the Uno’s hardware UART are pins 1/0. But they are shared w/the Uno’s USB-Serial adapter. My guess is that the code is using software to emulate a UART on the other pins to avoid a conflict w/any USB communication. Try swapping the Tx/Rx connections to pins 4/5. You can’t hurt anything doing this and swapped serial connections happen 93.7% of the time.
What level of current does scanner draw ?