Provide a link to the contact in your system, under which you fill out the form completely and get an unknown error. As part of this appeal, we will repeat your actions under the specified user and take further steps to resolve this issue.
I recommend that you create a separate appeal with a specific question/problem.
In this appeal, we are considering a question regarding the form
https://box.collarexpress.com.ua/mc/#/custompage/30, and questions about any other functionality within this form will only confuse and complicate the solution of this issue.