Hello!
I tried the above and it wasn’t working for me. I tried outputting $attachment_id in a print_r to see what was in there, and it was much more than just the ID. Seems like the full image’s meta data.
I eventually (90 minutes later) learned it was because my image field was set to return the image object and not the image ID.
Just posting here in case someone else missed this too.
Thanks for reading,
-Tim
