Converting nodejs HMAC to c#

Question

I have been given the following nodejs code the generates a signature. This signature is generated by a third party and I need to validate their signature on our backend API in C#. Their code is:

const crypto = require("crypto");
const secret = "..."; //do not share!
const actualSignature = crypto
  .createHmac("sha256", Buffer.from(secret , "hex"))
  .update(request.body, "utf-8")
  .digest("hex");

I have tried to implement in C# but I am uanble to get my signature to match theirs. Here's my code so far:

    public byte[] GetHash(string body, string secret)
    {
        var secretBytes = Encoding.UTF8.GetBytes(secret);
        var hexSharedSecretBytes = ByteToHexadecimalString(secretBytes);
        var hexSecretBytes = Encoding.UTF8.GetBytes(hexSharedSecretBytes);

        var hmac = new HMACSHA256(hexSecretBytes);

        var bodyBytes = Encoding.UTF8.GetBytes(body);
        return hmac.ComputeHash(bodyBytes);
    }

    private string ByteToHexadecimalString(byte[] buff)
    {
        return buff.Aggregate("", (current, i) => current + i.ToString("x2"));
    }

I would greatly appreciate some help.