Hi Tanvi,
it is best practise to use an available code exit/BAdI in order top call a BRF+ function.
So you have to investigate which BAdIs are offered in the transaction FB60 and which one is the most suitable for you to place the decision logic.
You can find a lot of examples how you can integrate BRF+ function in the documents of the overview page e. g. the integration of a BRF+ function for rebate vouchers in in SD
Hope that helps
BR
Christian