Hi Kunal,
Jmeter is bit difficult to use for API Testing.
You can use SOAPUI Tool for API Automation.
SOAPUI has both free as well as Commercial Professional versions (Pro).
You said API , what type of API SOAP or REST API?
If it is SOAP API and if you have WSDL file it is quite easy with SOAPUI Tool.
If it is REST API , and if you have Swagger API Definition file then REST Automation also Cake walk.
To use SOAPUI Open Source Free version , You must be good at groovy scripting( or Core java bcoz Groovy Script editors allows you to type Java Syntax).
If you have to automate too many API then i suggest you to Buy ReadyAPI (Latest SOAPUI Pro version) license from smart bear.
Single seat license may cost you 500-600 USD.
I have very good experience in API and Web Service testing , i am happy to Guide you.
-Rajendra