I don’t know why you are adding this
'capabilities' => array(
'manage_terms' => 'manage_trade_status',
'edit_terms' => 'edit_trade_status',
'delete_terms' => 'delete_trade_status',
'assign_terms' => 'assign_trade_status'
)
that has to do with the permissions for people to be allowed to do those things and depends on those capabilities existing. That is beyond what I was talking about.
I thought that you were using an ACF taxonomy field. To use a select field or whatever type of choice field that “trade_status” represents than in order to have the post updated with the correct terms you would need to use wp_set_object_terms() when saving the post (acf/save_post). It would be easier to use a taxonomy field unless there is a reason not to, like your field being in a repeater.
