Third repair and the patch keeps lifting at the edges

Almost always one of three things. First, surface prep. Any powder, silicone or shine product left on the area and nothing will ever bond, so both surfaces need degreasing properly and then leaving to flash off. Second, too much glue in one go. Thin coats, both faces, let each go tacky before you bring them together. A thick wet layer looks stronger and is much weaker. Third, pressure. Roll it down from the middle outwards with something smooth and keep the pressure on for longer than feels necessary.

Round your corners. A square patch has four points that catch on everything and each one is a place for a lift to start. Cut it as a circle or an oval, every time. That single change fixed this for me.

Also check where the tear actually is. If it is somewhere that stretches a lot when you move, a patch is fighting the material every time you wear it, and it will keep losing. That is not a technique problem, that is the wrong repair for the location.

It is on the inner thigh of a pair of leggings, so I suspect Sasha has just diagnosed me. That area does an enormous amount of stretching and I have been patching it flat while it is lying on a table.

That is the answer then. A patch applied flat on a table is sized for a garment at rest, and the moment you put it on, the rubber under it stretches and the patch does not. Either patch it with the area stretched to something like its worn state, which is fiddly, or accept that this one wants a professional repair. Inner thigh on leggings is one of the hardest spots there is.

Send it. I say that as someone who spent a whole winter repeatedly repairing a piece I could have had fixed properly for less than I spent on glue and evenings. There is no shame in it and repairers see this exact spot constantly.

Fair enough, that is three people saying the same thing and I have taken the hint. Sending it to be done properly and I will stop cutting squares out of a repair sheet at midnight.