How to dynamically pass values to HTTP request body (JSON format file).

Gatling (Open-Source)
1

Please consider the below jsonbody, and the it is saved as a json file in my project.

[
{
“access_token”: {
“original_client_id”: “spa-proxy-membership-ca”,
“channel_key”: “uqec-ca”,
}
}

]

So my question is that, how to dynamically pass the value of “original_client_id” from the simulation?
I have tried replacing “spa-proxy-membership-ca” with ${<variable_name>} as shown below, but it is not wokring.

[
{
“access_token”: {
“original_client_id”: “${<variable_name>}”,
“channel_key”: “uqec-ca”,
}
}

]

Please help.