Test your developer: Set up your chemicals – developer – stop – fixer – as before. Go dark and open the photo paper envelope; cut a sheet into several slices to be used as test strips. Return all but one strip to the light-proof package. Now turn on the lights. Immerse test strip in the developer as you watch. Because your darkroom lights are on, this test strip should now begin to blacken. If not, the developer is spent of contaminated or perhaps it is not the developer solution you think it is.
Re-mix a fresh developer following the mixing instructions. Verify that this developer is for photo papers. Repeat the test. Also, if the strip blackens, verify that you can identify the emulsion side versus the paper-base size.