The GPS system is one-way. The satellites broadcast signals. GPS devices receive and process the signals to determine their location.
Flat-Earthers often point out the fact we were unable to locate the ill-fated MH370 as ‘evidence’ GPS doesn’t work and therefore doesn’t exist. They are wrong. GPS satellites never receive any signal from GPS devices, and it is not possible for them to locate MH370.
GPS is a one-way system. The GPS satellites transmit signals but never receive them. GPS devices are passive, they receive signals but never transmit them.
MH370 periodically broadcasted its position using its ADS-B transmitter. But this is not part of the GPS system. At the time MH370 crashed, there were only ground-based ADS-B receivers, but there’s no coverage in the middle of oceans.
The fact that the GPS system was unable to locate MH370 is not ‘evidence’ GPS does not exist.