In UPS BX1000UXI power on/off button is flashing for every 2sec with beep sound?

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It indicates UPS is in Overload indication or may be short circuit at the output.
Check with customer how much watt load connected to the UPS (not exceeding 600W for BX1000UXI/1200W for BX2000UXI).
Disconnect non-essential equipment one device at a time to reduce the overload condition.
Restart the UPS until the overload indication or issue has been resolved.