Hi @toleanu
The true/false field will save it’s data as either a 1 or a 0. So the code update_field('topic_solved', 1, 4237)
should work correctly.
If the post (4237) does not already contain a value, you must use the field_key instead of the field name, however, it looks like you have already tried this.
Perhaps the code is not running due to a PHP error before it?
Thanks
E