Add new sales invoice and payment

Number of APIs: 6

1. customerlist.nv Get customerlist GET {{host}}/customerlist.nv?keyword=abc123456675

2. customer.nv Add new customer POST {{host}}/customer.nv?method=add

3. productlist.nv Get productlist GET {{host}}/productlist.nv?keyword=TP1,TP2

4. product.nv Add second new product POST {{host}}/product.nv?method=add

5. salesinvoice.nv Add salesinvoice POST {{host}}/salesinvoice.nv?method=add

6. salespayment.nv Add payment POST {{host}}/salespayment.nv