Have you researched the requirements of a VFT or of carnivorous plants in general?
Use no fertilizer or minerals...meaning no compost, no potting soil, too...nothing with nutritional value to it. Basically only sphagnum moss, sphagnum peat moss, coarse *silica* sand, perlite are the ingredients used in some combination for the grow mix. A standard mix is 50% peat moss and 50% perlite. Be sure and rinse any of this a couple of times with safe water.
Safe water... Only use rainwater, distilled water, RO water, etc.,...the water's TDS should be below 50ppm. Simple "drinking water" or "spring water" bought in jugs may or may not be safe...most of the time it isn't safe. Most people's tap/house water will kill the flytrap. As a last resort for water I *would* use water from a dehumidifier. A TDS meter is a simple gadget that sells here in the US on Amazon for US$15.00.
Keep the plant moist, not soggy. If it's really hot keep some water in it's tray (we've been running in the mid to upper 90F/33C range). Nice 75F-80F weather...no need for water in the tray. Don't let the growing medium dry out, though.
Flytraps require full sun..eventually. Windowsills usually result in failure. Do not instantly put a new trap out in full sun, though. Give it an hour in full sun for several days, then increase this time gradually over many days. A flytrap that has been inside and suddenly placed in full sun can sunburn. Gradually acclimate it back to where it came from...outside.
Too much food can kill the individual trap. Triggering the trap to "see it close" can end up in a trap that stops closing. They can only open and close *maybe* a half dozen times. A trap that stops trapping food is still producing important food for the plant through photosynthesis.
I'm not sure what is going on with your blackening leafs/traps...could have been a number of things. The good thing is that I see lots of new growth coming on. Be patient and let the plant settle in to it's new home. How large is the pot that it's in? Have you replanted it or is this the pot it came in.
Best wishes, have fun.