Push attachment ID into custom field

I'm using Gravity Forms with Advanced Custom Fields by Elliot Condon (If you haven't seen it before, check it out, it's awesome!) which for the most part works amazingly well, there's just one small thing I can't figure out...

Using the posts fields I've setup a form that catches data and adds a pending review post, all working well, however I was wondering if it is possible to push the attachment ID (for a post image field) into a custom field called 'featuredimage'?

The reason I'd like to do this is because in wp-admin that is how the ACF plugin catches the image I upload, I'd like the same thing to happen for users who are posting from the front-end using the gravity form I've setup.

Thanks for the reply!

Sadly it isn't the standard WordPress featured image, it's my own custom field I've setup as I don't believe the ACF plugin allows you to set it as a featured image.

I'm trying to do the same thing, and failing to get it to work. I've got a custom field generated by Advanced Custom Fields, with a meta_key of 'article-image'.

I've looked at the code referenced in the link post, and tried pasting a modified version into my functions.php file, but it's not updating my custom field. See code below.

http://www.pastie.org/3645280

I've double checked, and the form ID is 4. The images uploaded are attached to the post, so the problem isn't there, it just seems like it's not running the function. (I've tried modifying the last line to update_post_meta($post_id, 'article-image', 'hello'); just to test, and it still didn't update the custom field with 'hello')