When you want to share a web map with the embed viewer URL, you can not define the "alt_basemap" parameter to switch between 2 vector basemaps (in my case "World Navigation" and "World Imagery Hybrid"). Is there a workaround ?
Are you using URL parameters to define the alt_basemap parameter? If so, ensure that you also set basemap_toggle to True: Use URL parameters to modify embedded maps—ArcGIS Online Help | ArcGIS
Yes, I'm using alt_basemap combined to basemap_toggle but my issue is that alt_basemap doesn't have keywords for vector basemaps.
Retrieving data ...