QGIS Server Plugin Loading Problem: 'unexpected type 'sip.wrappertype'

Question

I'm using 3.6 qgis on the Ubuntu 18.04 server.

I made a plugin for limiting requests on our WMS server.

I'm having troubles loading the plugin I get always error:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/qgis/utils.py", line 577, in startServerPlugin
    server_plugins[packageName] = package.serverClassFactory(serverIface)
  File "/usr/share/qgis/python/plugins/request_limiter_filter/__init__.py", line 4, in serverClassFactory
    return RequestsLimiterServer(serverIface)
  File "/usr/share/qgis/python/plugins/request_limiter_filter/filter/requests_limiter_filter.py", line 27, in __init__
    serverIface.registerFilter( RequestsLimiter, 100 )
TypeError: QgsServerInterface.registerFilter(): argument 1 has unexpected type 'sip.wrappertype'