sensor:
- platform: command_line
  name: electricity_cost
  scan_interval: 86400
  command: curl \"https://api.octopus.energy/v1/products/AGILE-18-02-21/electricity-tariffs/E-1R-AGILE-18-02-21-F/standard-unit-rates/?period_from={{ now().year }}-{{ now().month }}-{{ now().day }}T{{ now().hour }}:{% if now().minute <30 %}00{% else %}30{% endif %}&period_to={{ now().year }}-{{ now().month }}-{% if (now().hour == 23) and (now().minute >=30) %}{{ now().day+1 }}{% else %}{{ now().day }}{% endif %}T{% if (now().hour == 23) and (now().minute >=30) %}00{% elif now().minute >=30 %}{{ now().hour+1}}{% else %}{{ now().hour}}{% endif %}:{% if now().minute >=30 %}00{% else %}30{% endif %}\"
  value_template: '{{ (value_json.results[0].value_inc_vat) | round(2) }}'
  unit_of_measurement: 'p/KWH'

Source; https://community.home-assistant.io/t/octopus-energy-agile-tariff/160458