Connecting to REST API with C#

Hello,

I'm new to NetSuite and have been fighting with trying to connect to the REST API using C# for a while now. I've downloaded the Postman collection and all of my calls are successful there, so I know I have the environment variables set up correctly. However, when I try in my actual code I get this error:

Invalid login attempt. For more details, see the Login Audit Trail

And when I check the audit log I get this message, which unfortunately doesn't help me pinpoint what's incorrect with the signature:

InvalidSignature

I've backed up a step, and although I know I can't hardcode the nonce and timestamp for my actual RestSharp call, I've temporarily hardcoded them just to see if I can get just the signature itself to match what's showing in Postman. (I'm not actually sure this is valid anyway, maybe it's not possible to generate the same signature twice the way this works?)