I have tried to use Ajax Search Pro. I have also installed the ACF plugin on the site. I do not get the possibility to make custom fields. When I make posts the area with custom fields is not there.
Ajax Search Pro does not affect the layout of the posts editor page, I believe by default ACF disables the default custom fields box. Try creating custom fields via ACF, or ask their support if there is a way to get the default custom fields metabox back to the editor screen. I’m sure there is a way to do that.