Assistance with Razer APIs - Login with Razer, Razer Silver

New developer hoping to create something cool with the Razer APIs. I've registered for a developer account and have created an app on the dashboard, so I have my client ID and secret, etc.

I'm using Postman to get an authorization code and received that so I could call the /userinfo endpoint, performed the Login with Razer and successfully received the openID. All that's great.

Now I'm trying to call the <removed by mod> endpoint to get my user's Razer Silver balance, but I'm not sure how to format my HMAC hash or what is my RazerServiceID as described at the bottom of p. 10 of the API documentation for 'Razer Silver Integration'.

The specific error I'm receiving is:

{
"statusCode": 74112,
"errorMessage": "Invalid hmac verification"
}

I'm unsure of how much I can share here so if someone from Razer support could PM me or advise, that'd be great!

Other questions:
1. In the developer documentation, when you're generating the HMAC hash, it makes reference to a 'shared key'. What is this key?
2. There's also a formatted JSON object where the same RazerServiceID is referenced. What are the key/value pairs that go into this object?

Thanks!