I need help!

I am gonna say your coco ph is off. 5.8 to 6.2 is range for coco grows. I use it regularly. It needs to be wet constantly as well in coco. Test your run off ph. If outside that range it will be issues. Plus at about 7 days they need light nutrition. Plus cal mag will be needed in grow. There is also no need to keep transplanting in a coco grow. Start or move it to final Potter. Coco is Hydro growing in a potter or bag. Your plants are too dry and mix about 30 percent perlite in to coco to improve drainage.

I don't see the problem?

Things to control : - The medium have to be moist but not wet. Youg roots (even older ones) needs oxygen. If the medium is too wet, the plant can't breath and it's dying. - Also careful of the Ph : 6.2 to 6.5 at this stage. - Most important : at this point, young plants don't have enough roots, so they drink/feed by the leaves. So it's really important to maintain RH arrount 80% at the begining. As your baby will grow, you'll progressivly down humidity. Progressivly... - control the environment temperature. Should be between 26 and 30°C.

AI Says : It is difficult to diagnose without seeing the plant, however, some possible causes for the issue could include overwatering, nutrient deficiencies, pH imbalances, or pests. It is also possible that the seed was not properly germinated or the plant is still in the process of adjusting to its new environment. Try testing the pH of the soil, checking for pests, and ensuring that your watering schedule is appropriate. I say : there was some watering issues with too much / too little and it and made the pH in the coco a bit different so the coco coir was too hot so it burned the seedling . Hope this helps ! 🚀

I guess I'm not seeing your worry here - the cotyledon is dying off but it's already done its job and is no longer useful... But I will say she probably needs a lot more humidity than she's being given? And it looks like you're not giving her enough water although it's REALLY tricky, at this point in their life, not to overwater and kill them. I wouldn't water right next to the seedling - I'd water out by the edges... and with coco, you need to make sure it's constantly moist (not WET, moist!). Since this is pretty obviously outdoors, you've also got to find a way to really increase the humidity around the seedlings - a dome or something that will have some air flow but keep the humidity high. Good luck!