In 1% of Salesforce Orgs, for unknown reasons, we are unable to retrieve the field ID's you need. Normally we scrape Salesforce's pages for the HTML, but if we can't do this, you will have to retrieve those values yourself. It only takes about 3-5 minutes.
First navigate to the Lead Fields page in setup.
Click on the DA_Form_Submitted field, and check the URL of that page. The field name is in the URL, after the last slash and before the question mark. You can see it in the screenshot below. Your value will be slightly different - please use the value you see in your Salesforce, not the value in the screenshot below.
You will need to do the same for the DA Token field.
These values should go in your Tracking Code and Hidden Fields (or in the relevant place in plugins, etc).