The expression return $this->actions returns the type hiqdev\php\billing\action\ActionInterface[] which is incompatible with the return type mandated by hiqdev\php\billing\order...Interface::getActions() of hiqdev\php\billing\order\ActionInterface[].
In the issue above, the returned value is violating the contract defined by the
mentioned interface.
Let's take a look at an example:
interfaceHasName{/** @return string */publicfunctiongetName();}className{public$name;}classUserimplementsHasName{/** @return string|Name */publicfunctiongetName(){returnnewName('foo');// This is a violation of the ``HasName`` interface// which only allows a string value to be returned.}}
In the issue above, the returned value is violating the contract defined by the mentioned interface.
Let's take a look at an example: