Hi there @benoitappaloosa,
Taking a look at your site, I tried submitting the sign-up form, and saw the same error message you mentioned:
Veuillez spécifier un ID de formulaire valide.
Please specify a valid form ID.
Checking the browser’s dev tools, I see that the form submission request was passing data like this:
action: mailpoet
api_version: v1
token: 8943187aa4
endpoint: subscribers
method: subscribe
data[0]: 1
data[1]:
data[2]: MP
data[3]: MP
data[4]: [email redacted]
data[5]: 2020
data[6]: Salarié d’exploitation agricole
data[7]: Porc
data[8]: Volailles
data[9]: 1
data[10]: 1
Notice the keys of each value being passed: data[0], data[1], data[2], and so on
Meanwhile, on my personal test site I see that they are all named:
action: mailpoet
api_version: v1
token: aa3e3f5804
endpoint: subscribers
method: subscribe
data[form_id]: 2
data[email]: [email protected]
data[first_name]: Kel
data[cf_5]: 1
Specifically, it’s very likely that the missing data[form_id] value in your case would be causing the “Please specify a valid form ID.” error message.
It’s unclear what is causing your form to be passing different data, but it is most likely coming from other code running on the site in either another active plugin or your theme.
As a next step, I’d recommend a conflict test to narrow down what is causing that behavior / error:
https://kb.mailpoet.com/article/204-how-to-test-for-plugins-conflict
