In order to fix the issue, navigate to Start > Control Panel > System and Security > Windows Firewall > Allow a program through Windows Firewall and check the box next to Wassapp. If you can't find the application in the Allowed programs and features window, press the Allow another program button, navigate to the installation directory, select the executable file and press Add.
After that, from the Advanced Settings select Inbound Rules > New Rule. Check the Port box, click Next, select All local Ports and follow the self-explained steps. Also, make sure that your security program doesn't block the connection. If the error persists, download and install the updated version of the program from the official web page. Also, you can use
firstname.lastname@example.org email address to get in touch with the developer.