Embed google maps with multiple location markers as iframe

Hi there,
I am very new to this. In order to include a google map with multiple location markers I followed the instruction on this website: Embedding a google map with multiple markers on your website

So I managed to generate an iframe that I embedded as Html component into my wix website. In editing mode everything looks great, but when I preview the site (sometimes not at first but after a while) the map disappears.
This is the iframe I am trying to include:

I read that for security reasons one cannot include http: links which would cause a similar scenario as I am experiencing, but the src here is https…

I did read about using the Google Maps API, which I am currently exploring but it seems quite a bit more complicated than the iframe solution.

I’d appreciate any tips.

See the example:

Multiple Markers in Google Maps

Embed Google Map on your site with multiple location markers , marker clustering, and custom controls using the HTML component.