Unable to get the correct base64 encoded digital certificate for ZATCA e-invoicing in python

Question

I am creating the xml for ZATCA einvoicing in python and i am stuck at step2 - generating digital signature and placing in the Signaturevalue tag .When i try to verify with zatca portal , it gives me the below error :

category : SIGNATURE_ERROR code :signatureValue message : wrong signature Value

Below is my code and the steps i am following in python :

f = ET.parse(xml_basic_out)
xslt = ET.parse(xml_transform_step1_xslt)
transform = ET.XSLT(xslt)
newdom = transform(f)
new_xml = ET.tostring(newdom,encoding ="utf-8") # Removed all spaces and comments from the original xml
# print(new_xml.decode())
xmldsig = chilkat2.XmlDSig()
canonXml = xmldsig.CanonicalizeXml(new_xml.decode(),"C14N",False)
invoice_hash_digest = sha256(canonXml.encode()).digest()
print(invoice_hash_digest)
invice_hash_digest_b64_encoded = base64.b64encode(invoice_hash_digest) 
print(f'Invoice Hash base64 encoded : {invice_hash_digest_b64_encoded.decode("utf-8")}')
with open(modified_invoice_hash_stp1, 'wb+') as o:
    o.write(invice_hash_digest_b64_encoded)



os.system('cmd /c'+'"'+openssl+'"'+' '+'dgst -sha256 -sign '+private_key+' -out ' +digital_signature_step2+' '+modified_invoice_hash_stp1)

with open(digital_signature_step2, 'rb') as f:
    data = f.read()
sig_b64 = base64.b64encode(data)
print(f'Digital Signature base64 encoded : {sig_b64.decode("utf-8")}')

In the above code , im doing the following:

1. reading the xml and Canonicalizing it
2. Creating the hash of the xml and storing it in the file
3. Signing the invoice hash (in bytes and not base64 encoded) with private key (pem) using openssl command
4. encoding the final output in base64

After doing all the steps im getting the output something like this : 'MEUCIQCaBTUxgZU/c1l7iNGE+Kzn+Mboj2XtYUiwUQZe9D51awIgbA3sfvKonKDLzGLj03OqoxfL0cPiGYTqtoDkiZjcOaY='

The above is not matching with zatca's expected output. Can someone please help me?