(if your unit is genuine Grandstream): https://www.grandstream.com/support/firmware – Search for "GXP21XX" or contact support for GM219S specifically.
She heard a knock. It was Old Man Hernán, whose farm sat on the hill. "My weather station is back," he said, bewildered. "It's showing barometric pressure from next week." firmware gm219s xpon full
Do not flash anything before completing this step. (if your unit is genuine Grandstream): https://www
(use with caution):
If you have access to a working "full" unit, you can dump the firmware via serial TTL or mtdblock backup. " he said