There is a knack to using and applying self adhesive patches.
If you just stick one on without any preparation, hoping for the best then they won't work.
You need to:
Prepare the area to be patched as you would do for a normal glue/rubber patch.
ie rub down the spot with rough paper.
After rubbing down, make sure the area to be patched is clean and dry.
Apply patch being careful not to touch the sticky side.
Press and hold the patch on to the innertube for at least a minute.
Rubbing down any creases and the edges.
Do not inflate the tube until it's back into the tyre.
This is what I do and haven't had a patch fail yet.