It's not possible to send submission using embedded forms when working in prod environment.

Setup:
1. SYMFONY_ENV set to prod and SYMFONY_DEBUG disabled.

Steps to reproduce:
1. Login as admin
2. Create a new Form with Simple Line Input and Button (Button action is "Show a message").
3. Publish it
4. Create a new Landing Page
5. Add an Embed block
6. Embed the Form created in steps 2/3
7. Open the form on frontend
8. Fill in the field and submit

Expected:
1. Message after submission is displayed
2. Submission is visible in the submissions list

Actual:
Nothing happens - landing page is refreshed, but submission is not sent.