Seems to be working for me on CUCM 11.5...
I can see that the related region name may have an extra 'n' which could throw things off assuming the other region (which exists?) is not also typo'd:
'regionName': 'testRegionn'
Can you confirm that you downloaded/placed the AXL WSDL files for 11.5 into the project?
Assuming you are using this project: https://github.com/CiscoDevNet/axl-python-zeep-samples
there have been some minor updates recently - it might be worth updating to see if any of the changes affect you.
E.g.:
git pull --rebase origin master
If you're still having issues, might enable the debug tracing option in the sample and share the output here. If all else fails, would suggest opening a DevNet developer support ticket so we can dig into the AXL logs on your CUCM - could be an environment issue: https://developer.cisco.com/site/support/