I just bought Ajax Search Pro for my multisite but I don’t understand why I have to enter my license number for each instance of the multi-site network and not just once for the whole network?
Also, when I try to enter the license number for another instance, it does not work.
You don’t need to enter the license key for each subsite – enter only on the main site. The license is only used for automatic upgrades, it does not limit the plugin in any way, so it is best to enter it on the main site only.