Hey @Amar-Azure-Practice - So, in order to establish a secure, reliable connection between your on-prem network and the Azure VNET (which your Function App runs inside of, in one of the subnets), you'll need to set up a site-to-site configuration, ideally. For more info on this guidance, please review: Connect an on-premises network to a Microsoft Azure virtual network
Alternatively, you can explore using Hybrid Connections, or On-Premise Data Gateway in conjunction with Logic Apps which can call your Function App as well.
If configurations involving VNETs seem overkill and you're not processing resource-intensive heavy payload, I would definitely go with a combination of On-Premise Data Gateway, Logic Apps, and Functions App option.