breathe cannot find C# interface - doxygen

Question

I'm trying to use doxygen, breathe and sphinx to generate documentation for a C# library. This is under Windows. The basic directory structure is:
docs
index.rst
conf.py
xml
xml output from doxygen
I'm running into the following error when I execute make.bat html:
C:\Programming\J4JLogging\J4JLogging\docs\index.rst:25: WARNING: doxygeninterface: Cannot find class "IJ4JLoggerConfiguration" in doxygen xml output for project "J4JLogger" from directory: ./xml
Here's the contents of conf.py
# import os
# import sys
# sys.path.insert(0, os.path.abspath('.'))
project = 'J4JLogger'
copyright = '2019, Mark Olbert'
author = 'Mark Olbert'
extensions = [ "breathe" ]
breathe_projects = {
"J4JLogger": "./xml"
}
breathe_default_project = "J4JLogger"
templates_path = ['_templates']
exclude_patterns = ['_build', 'Thumbs.db', '.DS_Store']
html_theme = 'sphinx_rtd_theme'
html_static_path = ['_static']
and here's the contents of index.rst:
.. J4JLogger documentation master file, created by
sphinx-quickstart on Tue Jun 11 16:33:34 2019.
You can adapt this file completely to your liking, but it should at least
contain the root `toctree` directive.
Welcome to J4JLogger's documentation!
=====================================
.. toctree::
:maxdepth: 2
:caption: Contents:
Indices and tables
==================
* :ref:`genindex`
* :ref:`modindex`
* :ref:`search`
Docs
====
.. doxygeninterface:: IJ4JLoggerConfiguration
:members:
The contents of the xml folder created by doxygen looks like this: