There are several common reasons for that, and you can fix them. Browsec usually shows possible reasons for failure and suggests solutions. In case you've missed it, see below.
Other VPN apps
If a VPN app is running, the system won't let another VPN app connect. Make sure to turn off all the dedicated VPN apps and those that may use VPN - for example, ad blockers. Also, some browsers may have built-in VPN, so make sure to turn it off. If you're not sure which app may interfere, just restart your device.
Anti-virus and firewall apps may prevent VPN apps from connecting to their servers, so make sure to whitelist Browsec there.
Wi-Fi hotspot settings
Browsec uses IPSec protocol and port 4500. Go to your router settings and make sure IPSec is allowed and port 4500 is open. If you can't access these settings, consider using another hotspot or mobile data.
Blocked by carrier
Some ISPs (internet service providers) block VPN. To check this, you can try another provider or Wi-Fi hotspot.