@ppatel
It seams like the server is not running.
Are you running NVDA on a 32-bit/ARM-64 machine. Sonata only works on 64-bit versions of Windows.
Otherwise, check if the server generated any logs in the following file path:
[NVDA config directory]\sonata\logs\sonata-grpc.log
If not, try running the following binary from a cmd window and report the output:
[NVDA config directory]\addons\sonata_neural_voices\synthDrivers\sonata_neural_voices\bin\sonata-grpc.exe