You have two options when it comes to workshop maps: either load a single map or create a collection.
Playing a single workshop map with friends on your dedicated Counter-Strike 2 server is a breeze once you locate the Workshop map ID. To find it, go to the desired workshop map on the Steam Website and check the URL for the ID.
Let's use this map for example: https://steamcommunity.com/sharedfiles/filedetails/?id=3070288532
As indicated, the map ID we'll be using is 3070288532. All you need to do now is to create a custom commandline and tick the box for Workshop Map.
Here is the link on how to create a custom commandline: https://billing.streamline-servers.com/knowledgebase/4169/Creating-Custom-Commandlines.html
Save the commandline and select it on the next page. Once selected, the commandline font will become bold.
