There are plenty of youtube videos that allow you to test Stereo sound by manipulating L & R Channel. Have you tried any such test?
Just search youtube for something like ‘stereo test left right’. Check and confirm if you are getting stereo or mono.
It could be that your input that you are checking may be centered mono, so in that case same sound will be heard from both speakers.
If Windows OS check the Balance setting in output properties.
If unsatisfied, in case amazon consider replacement if available.