Follow instructions as given:
- Install plugin
- Network Activate plugin
- Create sites as subdomain or subdirectory
Now map domains to sites as follows:
- IMPORTANT NOTE: You can not map domains to the main site!
- For each subsite, map by ID as Super Admin under Settings -> Domain Mapping
- For each subsite, go to Edit -> Settings and change Siteurl to the mapped domain. Do not change Domain, Path, or Subdomain under Info!
- Enjoy your mapped domains.