I think you need to use update_user_meta()
, I may be misunderstanding what you’re trying to do though.
EDIT (doesn’t work):
add_action( 'user_register', 'my_save_extra_fields' );
function my_save_extra_fields( $user_id ) {
update_user_meta( $user_id, 'deposit', 5 );
}
EDIT: WORKING SOLUTION:
add_action( 'user_register', 'my_save_extra_fields' );
function my_save_extra_fields( $user_id ) {
global $wpdb;
$cash=5;
$wpdb->update( $wpdb->users, array('deposit' => $cash), array('ID' => $user_id));
}