How to save multiple values with same meta_key, each value linked to another tag id

You can use insert_user_meta($user_id,'meta_key','meta_value');

when you want to get that keys, you can get like $keys = get_user_meta($user_id,'meta_key');

in $keys variable you get an array of all keys.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)