What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
Can you please ensure that you strictly followed these steps:
1. Allow iFrame on HTML fields.
On your Prestashop backend, go to your Administration Panel > Preferences > General > Allow iFrames on HTML Fields. Change it to "YES" and save it.
2. After copying your iFrame Embed Codes from JotForm, ENSURE that you:
a. Remove the script part, highlighted in yellow below.
b. Adjust the height (highlighted with violet below) based on the actual height of the form, you may need to preview your Prestashop page to see the entire form.
The message you're getting implies that you have pasted invalid content in Prestashop. Just make sure you follow the guide strictly, as is, and it should work.
Complete guide: How-to-add-a-form-to-your-PrestaShop-website
You may also try another method by using an iFrame Wrapper Tool which is offered as a Prestashop add-on. However, be advised that this is not free and you must purchase the plugin to enable it for use in your store.