Connection error is shown on FLS page
FLS shows connection error despite list of licenses in JetBrains Account is accessible from a web browser.
When connecting JetBrains Account via web browser you use browser's infrastructure including given connection permissions. FLS doesn't use it and attempts to contact JetBrains resources directly so there might be a need to allow license server software to contact JetBrains resources which are account.jetbrains.com and jetbrains.com accessed using HTTPS (port 443) protocol.
If you use MSI distribution, there is number of
.exe programs running by
JetBrainsLS service user which are
JetService.exe which might need to update their permissions.
There might also be a need to configure proxy for FLS software connections as described in proxy configuration instruction.