Apache JMeter - HTTPS POST Request for Auth Token 404/400'

Question

I'm trying to get apache JMeter to make an initial authentication call to generate a bearer token so that can be used in subsequent calls to do load testing. I'm having some issues getting the authentication call to work, specifically, I'm continuously getting a 404 (and now a 400) response from the server.

I don't think the problem is with my instance of JMeter, as I was able to make a GET call to the same server (just a different endpoint) and authenticate it by manually setting an authentication header using the header manager. I would use postman to make the auth call and get the token, then paste that into the header. That call works perfectly.

Here's my set up as is -- this is resulting in a 400. I think that's better than a 404? At least the call is able to find the server.

^^ The JSON body is exactly as it is from my postman request (which works)

I've tried: -just passing JSON body for username/password (404) -Passing the JSON body as multiple parameters (404) -Replicating the headers from the postman call using the header manager (404) -Using the authorization manager to send credentials -Following multiple "how to" guides online, and also looking around for troubleshooting tips.

For some reason, I cannot get JMeter to make this call. Please help.
Let me know if I'm missing any information. I'm running apache JMeter v5.3, Java 8.0_261-b12, macOS Catalina 10.15.7