Use Ninja Forms File Upload fields as the source of an ACF Gallery field, when using the Post Creation addon.

nf_fu_acf_gallery.php

<?php
add_filter( 'ninja_forms_create_post_meta_value', 'my_ninja_forms_create_post_meta_value', 10, 3 );

function my_ninja_forms_create_post_meta_value( $value, $post_type, $key ) {
	if ( 'gallery' !== $key ) { // change this string to match your ACF field name
		return $value;
	}

	return explode( ',', $value );
}

Add the above file to the wp-content/mu-plugins/ directory (create it if it doesn't exist).

Insert the File Upload mergetag as the meta value in the NF Create Post action, then add :attachment_id to the end eg. {field:file_upload_241:attachment_id}

Hi there :) !

Little question: How can we map a NF upload field with single ACF Image field? Can't find how...
Thank you :)

@cedriccharles4 you would do it in the same was as described here

Thank you, I've achieved my goal ;)