Need HMAC encode class written for Swift 5

Have API which accepts HMAC requests. Successful requests can be sent from Postman. Using Apple's CryptoKit (HMAC<SHA256>.authenticationCode) the resulting digest is different. The only thing I can figure out is successful HMAC encoding input is in Bytes format and the result is also in bytes format. Need developer who understands the nuances of HMAC SHA256 encoding in Swift.

Attached file "postman_prereq.txt" has the pre-request code that can successfully make API request in Postman.

It's this line in Postman/Javascript that is producing a different result than Apple's CryptoKit version-

var signatureBytes = CryptoJS.HmacSHA256(signature,secretByteArray);

versus

let signatureBytes = HMAC<SHA256>.authenticationCode(for: signature.data(using: .utf8)!, using: symKey);