php - I lose my twitter Access Token every time when I'm trying to unfollow users

I want to unfollow people who doesn't follow me. So I decided to use PHP-code.

$twi = new TwitterOAuth(...);

$friends    = (array)$twi->get("friends/ids", ["cursor" => -1, "screen_name" => "mylogin"]);
$followers  = (array)$twi->get("followers/ids", ["cursor" => -1, "screen_name" => "mylogin"]);

foreach ($friends['ids'] as $key => $val) {
    if (!in_array($val, $followers[ids])){
        $twi->post('friendships/destroy', ['user_id' => $user]);
    }
}
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Every time when I'm trying to use this code, I have only one unfollowed user. Then I have no access to API, cause I get an error.

Error 89: Invalid or expired token
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What should I do for not losing access token?