Open AR invoice - NonSAP System

Hi Experts

we are doing data migration of Open AR Invoice from legacy system to SAP

We have one customer invoice :1000 USD and the customer is partially paid for eg: 300 USD and there is an adjustment of 100$.

We have decided to migrate Open AR balance ONLY (i.e.) 600$ to SAP. But the business want to store total invoice amount of 1000$ + partially paid amount 300$ and adjustment of 100$ as well.. I didn't see any field in FB70 to store this information.

Could you advice how to achieve this requirement

Please consider as an urgent requirement and appreciate your kind input

Regard

Babu