How to link metas in front form?

[ombres-et-lumieres]

I created a front form to create a post, with somme metas added.

The metas are created in ACF.

And, I suppose I link them properly (see print screens). But the only ones to register are the basic ones: title and message that are, respectively, the title and the content ‘s post

And, by the way, why do I have to use a meta to register my image and not the feature image? For the “photo” field, I used “file” as I want to give the opportunity to upload a picture and not taking it from the library.