Toilet is not flushing

Check the flapper first. If it's ok, then go to Plan B, which I outline here:

I had this problem once. Flapper was lifting all the way, and still not enough water pressure coming down to adequately clear the bowl. More importantly, it was acting quite differently from when the toilet was new. Turned out the problem was mineral deposit buildup in/on the holes around and underneath the rim, and in the hole in the bottom (small hole where water comes out to start the flush siphon). That impeded the water flow enough to negatively affect the flushing action. If you get some citric acid from Amazon, or distilled white vinegar will work, but not as well, and do the following, your problem might be solved. The improvement was dramatic in my case. It should be noted that I took the toilet outside and turned it upside down and soaked all holes in muriatic acid. This stuff is dangerous to humans, animals, the environment, and everything else, so I'm offering that here only as full disclosure, not a recommendation!

Soak paper towels in the acid you choose (vinegar or citric acid solution) and stick them around the underside of the rim, so the acid can attack the minerals in all the small holes. Using a mirror, you can see the holes. Also, scoop and sponge all the water out of the bottom of the toilet, and pour 2 cups or so of vinegar or citric acid solution in the bottom. Let everything sit for several hours. Then, remove the paper towels and, using the mirror and a wooden stick of some sort, ream out every hole around the rim. Do the same for the hole in the bottom. The deposits should be partially dissolved, soft and easily removed by this point. Be finicky and thorough. If the deposits are still hard, repeat the acid procedure above. Flush the toilet, and be amazed!

Two more points...Citric acid comes as a powder. Mix 3-4 tablespoons to a cup of water to make the solution. Use vinegar full strength. Use a wooden stick for cleaning so you don't chip the porcelain, like might happen with metal. Let the acid do the work. If deposits are too hard to remove, they need more acid soaking. The acid will not hurt the porcelain at all, and will clean the stains in the bottom at the same time.