@Smruti Ranjan Nayak Thanks for reaching out. You might be using the Basic tier of APIM integrated with Application Gateway to expose on-premises APIs because it provides a cost-effective solution for development and testing scenarios. if you're looking for alternatives please refer: https://stackoverflow.com/questions/58836571/recommended-way-to-reach-on-premises-api-through-api-management-without-premium
But I would suggest you use standardv2 tier.
let me know incase of further queries, I would be happy to assist you.