ahah, went digging through the ACF code. I don’t know what ‘id’ is for, I didn’t even figure out where that ‘id’ value is used. ie. It may not be used at all, I didn’t dig that far.
$args = array(
'id' => 'my-form-id'
);
acf_form($args);
But I did figure out how to set the form ID
$args = array(
'form_attributes' => array('id' => 'my-form-id')
);
acf_form($args);