Unable to add wms in cesium

I tried wms layers in cesium from this site but im unable to add any.
I tried adding using below codes

var provider = new Cesium.WebMapServiceImageryProvider({

url : ‘https://services.ga.gov.au/gis/services/World_Political_Boundaries_WM/MapServer/WMSServer?request=GetCapabilities&service=WMS’,

layers : ‘World_Political_Boundaries_WM’,

parameters : {

transparent : true,

format : ‘image/png’

}

});

provider.readyPromise.then(function(){

console.log(“Success!”);

}).otherwise(function(error){

console.log(“Fail”, error);

});

imageryLayers.addImageryProvider(provider);

``

var imageryLayers = viewer.imageryLayers;

imageryLayers.addImageryProvider(new Cesium.WebMapServiceImageryProvider({

url : ‘http://gaservices.ga.gov.au/site_7/services/Topographic_Base_Map_WM/MapServer/WMSServer?request=GetCapabilities&service=WMS’,

layers : ‘Topographic_Base_Map_WM’,

parameters : {

service: ‘WMS’,

version: ‘1.1.0’,

request: ‘GetMap’,

transparent : ‘true’,

format : ‘image/png’

},

proxy: new Cesium.DefaultProxy(’/proxy/’),

}));

``

i also checked whether im getting response using promise, and also used cors filter plugin.

But im not able to add.

im always getting this kind of message in console

An error occurred in “c”: Failed to obtain image tile X: 0 Y: 0 Level: 0.

What im doing wrong.

I also checked the wms layers in arcgis they are working.

1) First Layer
I checked out the first wms - https://services.ga.gov.au/gis/services/World_Political_Boundaries_WM/MapServer/WMSServer?request=GetCapabilities&service=WMS
And if you look at the data in the <name> attribute - you will find a layer called 'Countries' but not 'World_Political_Boundaries_WM'. Is this the layer you are need? If so this should work:

var provider = new Cesium.WebMapServiceImageryProvider({
    url : ‘https://services.ga.gov.au/gis/services/World_Political_Boundaries_WM/MapServer/WMSServer’,
    layers : ‘Countries’,
    parameters : {
        transparent : true,
        format : ‘image/png’
    }
});
2) Second layer
I couldn’t get the other service to work however. I tried a few of them - You can check them out at
http://geopal.herokuapp.com/wms.html
You can see the layers in QGIS: but there are errors when you add them - Bathymetry is the only one that was displayed without an error.

Thanks for the reply.I checked the point you mentioned for the first layer.It worked.But why the second layer is not working.What could be the reason.