src/Core/CoreConstants.php
public static function getRedirectURL(array $settings){
        if(array_key_exists('redirectURL', $settings)){
            return $settings['redirectURL'];
        }else if(array_key_exists('RedirectUrl', $settings)){
            return $settings['RedirectUrl'];
        } else if(array_key_exists('redirecturl', $settings)){
            return $settings['redirecturl'];
        } else if(array_key_exists('redirectUrl', $settings)){
            return $settings['redirectUrl'];
        } else if(array_key_exists('RedirectURL', $settings)){
            return $settings['RedirectURL'];
        } else if(array_key_exists('redirectURI', $settings)){
            return $settings['redirectURI'];
        }else if(array_key_exists('RedirectUri', $settings)){
            return $settings['RedirectUri'];
        } else if(array_key_exists('redirecturi', $settings)){
            return $settings['redirecturl'];
        } else if(array_key_exists('redirectUri', $settings)){
            return $settings['redirectUrl'];
        } else if(array_key_exists('RedirectURI', $settings)){
            return $settings['RedirectURI'];
        }
        else{
            return null;
        }
    }
public static function getRedirectURL(array $settings){
        if(array_key_exists('redirectURL', $settings)){
            return $settings['redirectURL'];
        }else if(array_key_exists('RedirectUrl', $settings)){
            return $settings['RedirectUrl'];
        } else if(array_key_exists('redirecturl', $settings)){
            return $settings['redirecturl'];
        } else if(array_key_exists('redirectUrl', $settings)){
            return $settings['redirectUrl'];
        } else if(array_key_exists('RedirectURL', $settings)){
            return $settings['RedirectURL'];
        } else if(array_key_exists('redirectURI', $settings)){
            return $settings['redirectURI'];
        }else if(array_key_exists('RedirectUri', $settings)){
            return $settings['RedirectUri'];
        } else if(array_key_exists('redirecturi', $settings)){
            return $settings['redirecturl'];
        } else if(array_key_exists('redirectUri', $settings)){
            return $settings['redirectUrl'];
        } else if(array_key_exists('RedirectURI', $settings)){
            return $settings['RedirectURI'];
        }
        else{
            return null;
        }
    }
A helper method to get redirect URL. People may have a typo on the key name
@param Array $settings     The array contains all the key values
@return String | null      The redirect url developer provide