Please format your code properly by surrounding it with three backticks. See item 11.
If that’s real JSON coming from the PHP resource, you could try a REST sensor:
sensor:
- platform: rest
resource: http://192.168.1.210/123solar/programs/programmultilive.php
name: Produzione fotovoltaico
value_template: '{{ value_json[0]["GPTOT"] }}'
unit_of_measurement: "W"
scan_interval: 60