Problem with landingpage

First, thank you for your plugin, it’s really easy to use and gives a good result for me.

I have just a problem, when I add an email in the preview page and click to send the mail, a white page appears with the url : wp-admin/admin-ajax.php?action=ulpb_formBuilderEmail_ajax and all these informations appears : {“email”:”success”,”mailchimp”:”Inactive”,”convertkit”:”Inactive”,”drip”:”Inactive”,”activeCampaign”:”Inactive”,”campaignMonitor”:”Inactive”,”getResponse”:”Inactive”,”aweber”:”Inactive”,”markethero”:”Inactive”,”SendinBlue”:”Inactive”,”MailPoet”:”Inactive”,”ConstantContact”:”Inactive”,”WebHook”:”Inactive”,”MailRelay”:”Inactive”,”Zapier”:”Inactive”,”database”:true}

How can I fix the problem to just have the correct message “thank you, your mail has been successful sended”

Thank you so much for your help