Using Lib in Py 3 and beyond is not working

[SupreetBose]

Using sample code
xml_req = connections.Request(app, auth, xml_data).tostring()
Above line is giving error as below :
TypeError: can only concatenate str (not "bytes") to str
I am using Py 3.9 how should I proceed ? If I remove tostring from xml_req then I get the below error
TypeError: message_body should be a bytes-like object or an iterable, got <class 'oaxmlapi.connections.Request'>
My code that I used is as below to pull data
req = urllib.request.Request(url='Url Path', data=xml_req)
response = urllib.request.urlopen(req)
html = response.read()
print(html)
Any thoughts ?