When you create a form in blocs, the default behaviour is that it creates a submit link to to form script created by Blocs itself. In most cases, this works just fine because the script is uploaded to your server along with your website. This is the self-hosted option.
If you select the custom option, you can configure your form to submit to a third-party script, either hosted somewhere on your domain, or to a third-party hosting service. To do this, you would add the full URL of where your custom script is located. This will cause the submit button to direct your form results to the script you specified, from where it gets processed.
If your submit button isn’t directing to a form script, either self-hosted or a third party script, the submission will fail. If you configured your form to direct to the Blocs-generated script (self hosted) and you are not receiving anything, it may be that your host is blocking the email set up for receiving the form data. This can often be the case where the email address has a different domain to the host domain. Another issue may be that the sendmail function of the host isn’t working - some hosts may want you to set up a different system involving SMTP. If that is the case, you will probably need a third-party script so that SMPT setting can be set up.
The first thing you should check is that the Blocs application is creating the mail script and uploading it to your server. If you are testing locally - before uploading everything to your server, then the submission will fail anyway.The script has to be on your server for everything to work. Look at the export folder to make sure that it contains the formHandler.JS in the JS folder. and that the form_1.php is being published in the includes folder.