That stuck small download often points to a blocked or interrupted connection rather than a problem with your login itself. I would first run the installer as an administrator, temporarily disable any third-party antivirus or firewall just for the install attempt, and make sure you are on a stable wired connection if possible. It also helps to fully remove any partial Synapse installation, restart the PC, and then try a fresh installer. If it still stops at the same point, noting your Windows version and whether a VPN is active would help narrow down what is blocking that file.
I understand that you encountered an issue when installing Synapse. Can you send me a PM with your location/country so I can check for any alerts and use it when I forward your case to our Technical Team so they can investigate it?