QGIS » QGIS Application

First you need to check your URL how you call QGIS Server and try with capabilities request. Like Giovanni wrote, on Windows URL is different.
On normal installation this should give you XML response (assuming you are running Apache on port 80):

http://localhost/cgi-bin/qgis_mapserv.fcgi.exe?SERVICE=WMS&VERSION=1.3.0&REQUEST=GetCapabilities

If you receive Page not Found (404), something is wrong with your Apache configuration. Repeat setup:

https://docs.qgis.org/testing/en/docs/user_manual/working_with_ogc/server/getting_started.html#installation-on-windows

I am now able to request the capabilities of the Service in the Browser.
URL: http://localhost/cgi-bin/qgis_mapserv.fcgi.exe?SERVICE=WMS&VERSION=1.3.0&REQUEST=GetCapabilities

However. When trying to add the WMS to QGIS (http://localhost/cgi-bin/qgis_mapserv.fcgi.exe), the connection is loaded showing the correct name of the instance. The Problem of the layers still occur. This means that the name of the layer is empty and when adding it to the map the very same error is shown:
'[Fehler: Error transferring
http://localhost/cgi-bin/qgis_mapserv.fcgi.exe?SERVICE=WMS&VERSION=1.3.0
&REQUEST=GetMap&BBOX=2686652.655435386114,1241070,2694050,1249254.345484995749&CRS=EPSG:2056&WIDTH=639
&HEIGHT=707&LAYERS=WMS_Test&STYLES=&FORMAT=image/png&DPI=192&MAP_RESOLUTION=192&FORMAT_OPTIONS=dpi:192
&TRANSPARENT=TRUE - server replied: Not Found; URL: http://localhost/cgi-bin/qgis_mapserv.fcgi.exe?
SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&BBOX=2686652.655435386114,1241070,2694050,1249254.345484995749&
CRS=EPSG:2056&WIDTH=639&HEIGHT=707&LAYERS=WMS_Test&STYLES=&FORMAT=image/png&DPI=192&MAP_RESOLUT'

For the connection of the DB I have saved the password and user within the project.

Louis Leguan wrote:

I am now able to request the capabilities of the Service in the Browser.
URL: http://localhost/cgi-bin/qgis_mapserv.fcgi.exe?SERVICE=WMS&VERSION=1.3.0&REQUEST=GetCapabilities

However. When trying to add the WMS to QGIS (http://localhost/cgi-bin/qgis_mapserv.fcgi.exe), the connection is loaded showing the correct name of the instance. The Problem of the layers still occur. This means that the name of the layer is empty and when adding it to the map the very same error is shown:
'[Fehler: Error transferring
http://localhost/cgi-bin/qgis_mapserv.fcgi.exe?SERVICE=WMS&VERSION=1.3.0
&REQUEST=GetMap&BBOX=2686652.655435386114,1241070,2694050,1249254.345484995749&CRS=EPSG:2056&WIDTH=639
&HEIGHT=707&LAYERS=WMS_Test&STYLES=&FORMAT=image/png&DPI=192&MAP_RESOLUTION=192&FORMAT_OPTIONS=dpi:192
&TRANSPARENT=TRUE - server replied: Not Found; URL: http://localhost/cgi-bin/qgis_mapserv.fcgi.exe?
SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&BBOX=2686652.655435386114,1241070,2694050,1249254.345484995749&
CRS=EPSG:2056&WIDTH=639&HEIGHT=707&LAYERS=WMS_Test&STYLES=&FORMAT=image/png&DPI=192&MAP_RESOLUT'

aren't you missing the "map" parameter?

I have tried different URL's like: http://localhost/cgi-bin/qgis_mapserv.fcgi.exe?request=getcapabilities&service=WMS&version=1.1.1. The layer is still not shown and the same error occurs..
http://localhost/cgi-bin/qgis_mapserv.fcgi.exe?VERSION=1.3.0&map=C:/OSGeo4W/apps/qgis/bin/WMS_Test.qgs isn't working at all.
The map parameter is usually not included when adding a Geoservice I thought.

The map parameter is usually not included when adding a Geoservice I thought.

not that is not completely true: unless your project file is exactly in the same folder where the qgis_mapserv.fcgi executable is then you must specify the map parameter map=/path/to/project.qgs

Giovanni Manghi wrote:

The map parameter is usually not included when adding a Geoservice I thought.

not that is not completely true: unless your project file is exactly in the same folder where the qgis_mapserv.fcgi executable is then you must specify the map parameter map=/path/to/project.qgs

anyway there is another ticket about qgis server 3.4.4 on Windows that states that the program is broken, so this ticket may just be duplicate of it.