Multisite Different Domains

Good day

I am having trouble creating a multisite for different domain names. I have 4 domains. lets say domain1.co.za, domain2.co.za, domain3.co.za and domain4.co.za. I need domain1.co.za to be my main domain and link the other 3 to that domain. But I cant by the life of me figure out what to do. All the advice I can find include sub domains and none of my sites are sub domains at all. I have the plugin MU domain mapping installed and have tried following the instructions but I cant get the sites to detect one another at all.

Does anyone have any advice how I can get this up and running?