'Can't resolve target of expression' with some variable in the path

Code:
require_once $_SERVER["SOME_VAR"] . "/api/some.php";

Warning:
Can't resolve target of expression '$_SERVER["SOME_VAR"] . "/api/some.php"'
Path 'api' not found


'api' dir located in root folder of project, and $_SERVER["SOME_VAR"] defines where root folder is located
Is there are a way to avoid this warning message?