Jmeter does not send JSON data in POST

To send a POST HTTP Request with the JSON Data inside the body, need to add,

• HTTP Header Manger into your request and set the name as 'content-type' and value as 'application/json' this will attached into HTTP request header and what ever the data inside your request body will send as json format.

Image 1:Set HTTP Header Manager,

Image 2:Set HTTP Request Body Data

1. Make sure your HTTP Header Manager is configured to send Content-Type header with the value of application/json
2. Given you have samplers like "home page" and "login" it might be the case you're missing HTTP Cookie Manager
3. The most straightforward way to see what's wrong is to capture requests sent by Postman (whatever it is) and JMeter by a sniffer tool like Wireshark, identify the differences and configure JMeter accordingly.
4. Finally, it looks like you're using some developer snapshot so approach to pass JSON payload as 1st argument without name might not work. Try switching to "Body Data" instead.
5. If above steps won't help update your question with screenshots of View Results Tree listener (all 3 tabs) and Postman

Check out Testing SOAP/REST Web Services Using JMeter for more tips.

This solution from Dmitri T, really worked for me.

Make sure your HTTP Header Manager is configured to send "Content-Type" header with the value of "application/json".