Freshservice Asset Type Fields

We are developing a freshservice custom app for one of our customers in which assets needs to be synced from an external source to asset inventory. In that, pre-requisite will be all the asset types should be present in the Freshservice. For creating the asset types we have the public APIs available.

But for creating the type fields inside each asset type there is no API available in the API Documentation. As of now we have 64 asset types that needs to be created and 20 fields to be created for each asset type. It will take more manual effort for the development and also excessive manual effort for our customer during the production deployment.

Is there any other internal APIs available ? Can you please help us with this problem statement ?