Cornerstone Forms Dropzone attachments feel unreliable compared to File Input

Support
#1

Hi Themeco team,

first of all: I really appreciate your work and I’m generally a big fan of Cornerstone and the direction you are taking with Forms.

That said, I’m struggling quite a bit with file uploads in Cornerstone Forms. The current setup feels more complex and less predictable than I expected from a paid Forms extension, especially for a feature that appears to be part of the advertised Forms workflow.

My use case is simple:

I want users to upload one or multiple files and send those files as attachments in the administrator email.

What I found:

  • A normal single File Input works.
  • The file can be selected in Email Action → Attachments → Type: Form Data.
  • The email attachment works when the Email Action runs before the File Upload Action.

However, Dropzone behaves differently:

  • The Dropzone field is not always available in the Email Action attachment field selector.
  • When using a “File Upload Exists” condition, the Dropzone field disappears from the selector.
  • Without that condition, the Dropzone field may appear, but submitting the form causes this error:
preg_match(): Argument #2 ($subject) must be of type string, array given

From the rendered markup it looks like Dropzone submits files as an array, even when only one file is allowed:

<input type="file" name="project_files[]" multiple>

So it seems the Email Action expects a single string/path, while Dropzone provides an array.

My actual requirement is multiple file uploads, so Dropzone would be the obvious and expected UI for this. But right now it does not feel reliably usable for Email Action attachments.

Could you please clarify:

  1. Is Dropzone officially supported as an attachment source for Email Actions?
  2. Are multiple Dropzone uploads supposed to be sent as email attachments?
  3. If yes, what is the correct native setup?
  4. If no, could this limitation be documented more clearly?

I may be missing something, but from a user perspective this currently feels a bit immature compared to the rest of Cornerstone. The Form setup is powerful, but for a basic task like “upload files and send them to the admin”, I expected a more straightforward workflow.

P.S. Apologies if the wording sounds a little too polished — I used AI to help structure the issue clearly. The problem itself is real and reproducible in my setup.

Thanks for your help.

#2

Hey @egon2358,

1. Is Dropzone officially supported as an attachment source for Email Actions?

No, not natively under the “Form Data” attachment type.

While a standard File Input works because it uploads a single file, the Email Action’s native attachment handler is not built to support the array-based structure of Dropzone.

2. Are multiple Dropzone uploads supposed to be sent as email attachments?

No, this is currently a limitation in the native implementation.

3. If no, could this limitation be documented more clearly?

We’ll either document this or list a feature request to support multiple dropzone uploads.

Thank you for your questions.