At the moment we are using the Stamen Toner Labels tile server to display additional information over various World Imageries.

The problem is, Stamen.TonerLabels is now closing:

https://maps.stamen.com/stadia-partnership/

Possible alternatives

Find one here:

https://leaflet-extras.github.io/leaflet-providers/preview/

Example:

https://leaflet-extras.github.io/leaflet-providers/preview/#filter=CartoDB.PositronOnlyLabels

var CartoDB_PositronOnlyLabels = L.tileLayer('https://{s}.basemaps.cartocdn.com/light_only_labels/{z}/{x}/{y}{r}.png', {
	attribution: '&copy; <a href="https://www.openstreetmap.org/copyright">OpenStreetMap</a> contributors &copy; <a href="https://carto.com/attributions">CARTO</a>',
	subdomains: 'abcd',
	maxZoom: 20
});

The problem is: this version is not included in our version of leaflet-providers.js so we also must update it, in case.