add a circle overlay

tried to use the code https://gmap3.net/api-circle.html but it doesn’t work.

Indeed, that’s because you are likely trying to attach the circle prior to the initialisation of the map object.

I don’t think there is a map event fired when the map is ready.

I will need to expose the map object with a custom event. Let me test this on my server and I will provide you with a solution.

v1.6.0 is just released and has new functionality that exposes the js map objects using events.

If you are using the CF7 Smart Grid UI editor plugin, you will get in-line helper codes as this plugin now integrates with the UI editor, simply copy the js helper codes to your js file (see screenshot #17 on the smart grid plugin page). Else, you can see FAQ #10 oof this plugin page to for an example js code.