qgis - Make WMS layer background transparent in Leaflet

I have inserted the following layer from a GeoServer WMS in the following Leaflet map

:

var nexrad = new L.TileLayer.WMS("URL", {
    layers: 'Wrecks:WrecksGreaterNorthSea',
    format: 'image/png',
    transparent: true

});

but the background is not transparent. I have tried to set it by modifying the tiff image with QGIS creating a transparency band but it does not work. I have a second WMS layer in the map but I do not have this problem with this one.

Could you help me solve this issue, please?