In Pokemon Sun & Moon, wild Pokemon could call for help via SOS calls indefinitely. This meant that each turn, a wild Pokemon had a chance to call for help. 
However, in Pokemon Ultra Sun & Ultra Moon, this was nerfed so that wild Pokemon could only call for help once per battle. However, by using an Adrenaline Orb in battle, this would allow wild Pokemon to call for help indefinitely again, as they originally did in Sun & Moon.
This plugin allows you to set either style of SOS call frequency through a setting found in the plugin's Settings file. In here, you will find a setting called LIMIT_SOS_CALLS_TO_ONE. When this is true, SOS frequency functions as it did in Ultra Sun & Ultra Moon; meaning wild Pokemon will only call for help once, but can call indefinitely if an Adrenaline Orb is used.
If this setting is set to false, then SOS frequency functions as it did in the original Sun & Moon; meaning wild Pokemon have a chance to call every turn indefinitely.
By default, this setting is set to true, so that the SOS mechanic functions as it did in Ultra Sun & Ultra Moon. But you may change this if you prefer how the SOS mechanic originally worked.