Composite or Mixed Supply - Goods and Services Tax - GST

Instruments viz. diagnostic kit are supplied on Free of Cost basis to the customer under a Delivery Challan without payment of GST with an assurance of certain amount of business with regard to reagents used in these instruments. The value of such instruments is approx. Rs. 10 Lacs. To install the said instruments at the customer site, amount towards Installation and Commissioning is recovered from the customer under Tax Invoice. Value of the invoice is Rs. 1.25 Lacs and GST of Rs. 0.23 Lacs is charged on the same. Will this be treated as Composite or Mixed Supply and if yes, whether GST will be demanded on the free of charge instruments supplied without payment of GST?