Create an HMAC SHA256 hash for HTTP Signature in Swift

Question

I'm fairly new to Swift and am currently working on HTTP signatures. I'm using the approach from this answer but the implementation doesn't work and gives me a different hash than I get from an alternate implementation I have in Python (which I'm more familiar with but have only rudimentary knowledge of cryptographic principles).

Here's the Swift code:

let secret = "my-secret"

let headersForSig = "single-string-combining-headers-with-\n"

let keyForHash = SymmetricKey(data: secret.data(using: .utf8)!)
let signatureHash = HMAC<SHA256>.authenticationCode(for: headersForSig.data(using: .utf8)!, using: keyForHash)

--EDIT--

Following @sulthan's comment below, changed the final formatting of the signature to this:

let basedSignatureHash = Data(signatureHash).base64EncodedString()

This all follows the above linked answer. But the API call with this signature doesn't work and doesn't look like the hash from the Python implementation.

An alternate approach in Python does work:

sig_value = "".join(list-of-headers-for-signature)

sig_value_string = str(sig_value)

sig_value_utf = bytes(sig_value_string, encoding='utf-8')

secret = base64.b64decode("my-secret")

hash_value = hmac.new(secret, sig_value_utf, hashlib.sha256)

signature = base64.b64encode(hash_value.digest()).decode("utf-8")

This works and unsurprisingly the signature hash is different! How can I mimic this approach in Swift? Or is there something else like order of headers that might be different between the two that's messing this up?

The structure of setting up the request object is nearly identical in both languages: create a request object with the target URL, add the required non-signature headers, then create the signature and add it as the last header.