I need help when it comes to adding custom model as a block

Hi

I've been trying to make a custom model block in Mc creator and I've been stumbling upon some problems.

If I use a Json file for my model it simply won't appear in my inventory, but if I use an Obj+Mtl file it will appear in my inventory, but when i place down the object it shows a whole block with a missing texture.

How can I fix this issue?

best regards Val.