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Why Special Steps are Necessary
While Gnome Software Center is available in Pamac, many Arch users warn against using it because Gnome ships an embedded update service along with it. Since Antergos already has an update service, adding another ones causes them to conflict and possibly mess up the system. Thus, to avoid this confliction, there is a script that installs it for you with the necessary modifications already in place. It can be found here.
How to Fix It
The script disables the entire update service within the Gnome Software Center so that it cannot interfere with anything. To download it, simply follow the above link and click Download Here. The file that is then presented is the desired script, which installs the software center and then implements the tweaks to disable the update service automatically. Since it is only a script, once it is downloaded make it Executable and then simply click it and Run in Terminal. After that, it should automatically do all of the rest of the work for you.
If you don't know how to make the script Executable, just head over here for some help.