Error when adding new subscriber

Hi,

I have moved my website from a test-server to an online-server with a new domain.

Now the MailPoet signup-widget is not working anymore.

When I try to add my email address and click the submit-button, I’m getting this error:

Oops! There is a problem with this form:
textStatus:error
errorThrown:Not Found
responseText:
(Here it’s showing a 404-page)

What can be the problem?

Thanks for your help!

https://wordpress.org/plugins/wysija-newsletters/