Additional fields in a temporary dataset are not present

Hi,
I have InvcHead as dataset, I have created a temporary dataset XYZInvcHead with some extra fields.

I copied InvcHead to XYZInvcHead with merge option and pass this dataset in a erp-rest function, but in function I didn’t receive the additional fields which are present in XYZInvcHead.

Please guide me, how I can handle this situation.
Regards