hmac.digest gives UNEXPECTED_ERROR

I am trying to implement a JSON Web Token, and thus trying to get crypto.hmac to work, but I'm having issues with it. I made a password tool from a modified version of the suitelet from this thread, and I have a password guid that I have generated and restricted for use on my custom script id, that I am using in that custom script. However, each time the code gets to the .digest() call, it throws UNEXPECTED_ERROR. I'm still new to SuiteScript and I'm not sure what I am doing wrong:

       var sKey = crypto.createSecretKey({          guid: "6332f5d7575a481388a24b924292d552", // restrictToDomains=['system.sandbox.netsuite.com'], restrictToScriptIds=[<MY SCRIPT ID>]          encoding: encode.Encoding.HEX        });        var hmacSignature = crypto.createHmac({          algorithm: crypto.HashAlg.SHA256,          key: sKey,        });          hmacSignature.update({          input: encHeader + "." + encPayload,          inputEncoding: encode.Encoding.UTF_8        });        var signature = hmacSignature.digest({          outputEncoding: encode.Encoding.BASE_64_URL_SAFE        });        return encHeader + "." + encPayload + "." + signature;