Unable to get Access Token in Jmeter - rest

Question

I'm trying to get an access token in Jmeter, and it works fine with postman, but I end up with an error in response in Jmeter saying
{
"error":"invalid_grant",
"error_description":"The provided authorization grant (e.g., authorization code, resource owner credentials) or refresh token is invalid, expired, revoked, does not match the redirection URI used in the authorization request, or was issued to another client",
"status_code":400
}
Postman Body
Header in postman
I get access token as json response when i post this request
My setup in Jmeter looks as follows:
HTTP request
HTTP Header
I get following response when i run the test in jmeter
{
"error":"invalid_grant",
"error_description":"The provided authorization grant (e.g., authorization code, resource owner credentials) or refresh token is invalid, expired, revoked, does not match the redirection URI used in the authorization request, or was issued to another client",
"status_code":400
}

Answer 1

Given you send the same requests you should be getting the same responses so most probably the requests differ somewhere somehow.
You need to compare raw request body from Postman and the same from JMeter using View Results Tree listener
One obvious difference is missing Accept header in JMeter.
It might be the case that variables like ${_code} and ${base64HeaderValue} don't have their respective values, you might want to check them using Debug Sampler
And last but not the least, if your request works in Postman you can just record it using JMeter's HTTP(S) Test Script Recorder, just configure Postman to use JMeter as the proxy
And next time you run the request in Posman JMeter will capture it and store the relevant HTTP Request sampler (with the HTTP Header Manager) under the Recording Controller