Quick answer
If the VPN is not connecting, the most common culprits are the local network or WiFi, wrong password or certificate, blocked port on the router or firewall, as well as an outdated VPN app. First check if the internet works without VPN, then re-enter your login details and update the client, and only then change advanced settings.
How to recognize the problem
- VPN client shows "Connecting" and eventually an error or the connection drops immediately
- Message about incorrect username, password or expired certificate
- VPN connects but there is no access to the internet or internal resources
- Connection works on mobile internet but not on home WiFi
- VPN constantly disconnects after a few minutes of operation
Most common causes
No stable internet connection
The VPN tunnel cannot be established if the underlying connection drops or is very slow. Check if the internet works without VPN.
Incorrect login details or expired certificate
Changed password, expired certificate or wrong profile are the most common reasons for authentication errors.
Blocked port or firewall
Router, ISP or antivirus may block the port used by the VPN (e.g. UDP 500 or 4500).
Outdated VPN app or driver
An older client version may be incompatible with an updated server or operating system.
Incorrect time and date on the computer
A large system time deviation breaks TLS certificate validation and prevents connection establishment.
Step-by-step fix
- 1
Check internet without VPN
Turn off the VPN and open several websites. If the internet does not work, first solve the network or WiFi issue. If it works, continue.
- 2
Re-enter login details
In the VPN client, if available, select
DisconnectorLog out, then selectConnectorSign inagain and enter your username and password. Pay attention to uppercase and lowercase letters and the keyboard layout (Serbian/English). - 3
Update the VPN app
Check if the client is the latest version. Look for an update option in the app or download it again from the official website. Then restart the computer.
- 4
Check date and time
In Windows, go to
Settings > Time & language > Date & timeand enable automatic setting. On macOS:System Settings > General > Date & Time. Incorrect time often causes certificate errors. - 5
Temporarily disable firewall and check antivirus
Do this only briefly for testing and do not leave protection disabled. In Windows, open
Windows Security > Firewall & network protectionand temporarily disable the firewall for the private network. If the VPN starts working, immediately re-enable it and add an exception for the VPN client. If you suspect antivirus, check its blocked applications list and add an exception instead of disabling protection. - 6
Change network or port
If the VPN works on mobile internet but not on home WiFi, try another network. Change the port or protocol (e.g. TCP 443 instead of UDP 500) only if the client and server support it and according to administrator instructions.
- 7
Reset the VPN client
Before resetting, note down profile settings because saved profiles will be deleted. Look for the
Resetoption in the app or delete saved profiles and re-enter them. In Windows, you can remove the client viaSettings > Apps > Installed appsand then reinstall it from the official website. - 8
Check the certificate
If you use a certificate, check that it has not expired. In Windows, open
certmgr.mscfor the current user orcertlm.mscfor the computer and check the expiration date. If expired, request a new one from the administrator.
If nothing helps
If you have tried all steps and the VPN still does not work, contact IT support or the VPN administrator. They can check if the server is available, if your account is active and if settings have been changed in the meantime. In a business environment, it is often necessary to add a firewall exception or update the profile on the server. Manual registry editing or installing unknown VPN tools is not recommended because it can compromise security. If you use the VPN to access internal resources, notify the responsible persons that you cannot work so they can provide alternative access or a temporary solution.
How to prevent it
- Regularly update the VPN client and operating system
- Use a stable internet connection and check WiFi signal
- Do not change network settings manually without need
- Monitor certificate expiration dates and renew them on time
When to call a professional
If the VPN does not work even after all steps and you need it for work, contact IT support. They can quickly check the server side and your account, as well as apply advanced settings without risk.
IT infrastructure maintenance · Servers, networks, backup, security and helpdeskFAQ
Why does VPN work on phone but not on computer?
Most likely the difference is in the network or settings. Check if the computer is on the same WiFi network, if the firewall blocks VPN and if the client is updated. Sometimes the problem is incorrect date or certificate.
Is it safe to disable firewall to make VPN work?
Temporary disabling is acceptable for testing, but do not leave the firewall permanently disabled. Instead, add an exception for the VPN app or port.
What does the error "VPN server not available" mean?
This usually means the client cannot connect to the server, either due to network, blocked port or because the server is temporarily down. Check internet connection and try later or change the port.