If you have been contacted by a Reactive Drop Team admin to create a donation item, perform the following steps:
Open the developer console in Alien Swarm: Reactive Drop. This is done using the ` key. If you have not already enabled the developer console, it can be enabled in Keyboard settings.
Enter the command:
ugc_curated_create
The Steam Overlay (or your system web browser if you have the Steam Overlay disabled) will open to a new Steam Workshop curated item.
Edit the title of the item and set up the revenue split on the website.
Send the Reactive Drop Team admin a link to the item you created.
Curated items can be viewed at https://steamcommunity.com/workshop/browse/?appid=563560&browsesort=curatedadmin§ion=mtxitems&p=1&browsefilter=curatedadmin&actualsort=mostrecent. Create payment rules by following the instructions at https://partner.steamgames.com/apps/enternewworkshoppaymentrules/563560/.