Wireless issues are often resolved with a few quick checks before escalating.
Quick checks
Move closer to the access point, confirm the correct network is selected, and restart your device's Wi-Fi. Check whether other devices are affected.
Restart the access point
If you're authorized, power-cycle the affected access point. Wait two minutes for it to fully restart.
When to contact BTS
If the issue persists or affects many users, submit a support request with the category 'Internet or network'. Include the location and access point name if known.