This website allows you to recursively flatten your JSONs.
This is done in a way that guarantees MOMI compatibility for Fields of Mistria's __fiddle__.json derived files.
Make sure you only include the not flattened parts in your input (example below).

Report issues over at https://github.com/FoMTinkering/Flattener/issues if the error message states the algorithm made a mistake. Or just check the GitHub page to help out with the organisation! (not affiliated with NPCStudio)