Fatal error on single player load

I am not sure what is going on, this is my first mod.

I created a copy of the grappling hook ammo. When equipped to a crossbow it creates a copy of the grappling crossbow that does not consume ammo on firing.

Also created an engram for the new ammo

Followed youtube tutorials on how to cook the mod and everything. Everything works in the dev kit, I can learn the engram craft the ammo and it all works

Cooked the mod, no errors, lots of warnings, uploaded it, subscribed, set it in singleplayer, Crashes at C3-Near-WIP

Any help is appreciated. Ill provide whatever screenshots are needed.

I recooked the mod and now it is working.

However

For some reason the engram for the custom item shows up in single player, but on everyone’s servers the engram doesn’t show up…What could cause that?

Did you use the “Additional Engrams” list?
or the “Master” lists, I had this issue as well thanks to outdated tutorials, you just need to subscribe your engram to the Additional Engrams lists, item is not needed(By this I mean you don’t need to add the item to a list, the engram covers that. At least it’s worked for me so far), however I believe there is an Additional Dino and Structure list so if you’re working with those too, make sure you add them into those respected lists as well.