This is the expected return value format for rate scripts:

{
  'meta_data'?: <dict>,
  'rate': <dec>,
  # One of 'per unit' or 'per reservable'.
  'rate_basis': <str>,
  'rate_description': <str>,
  'rate_int'?: <int>,
  'prorate_half_interval_multiplier'?: <dec>,
  # One of 'per hour', 'per use', 'per block', 'each', 'per request',
  # 'per session', 'per sample', 'per day', 'per week', 'per month'.
  'rate_unit': <str>,
  'sku?': <str>,
  'tax_code'?: <str>,
  'tax_note'?: <str>,
  'tax_rate'?: <str>,
}

When executing a rate script, the base rate is also accessible in the script iself, under the context variable script["rate"]. The format of this object is slightly different:

{
  'blackouts': {
    'blackout_id': <int>,
    'weekday': <int>, # Integer from 0-6, representing Monday-Sunday.
    'start': <str>, # HH:MM:SS where HH is 24 hour time
    'end': <str>, # HH:MM:SS where HH is 24 hour time
    'reason': <str>,
  },
  'currency'?: <str>,
  'currency_decimal'?: <str>,
  'currency_thousand'?: <str>,
  'currency_code'?: <str>,
  'invoice_automatically': <bool>,
  'meta_data'?: <dict>,
  'public': <bool>,
  'rate': <dec>,
  # One of 'per unit' or 'per reservable'.
  'rate_basis': <str>,
  'rate_description': <str>,
  'rate_duration_maximum': <int|None>, # Seconds
  'rate_duration_minimum': <int|None>, # Seconds
  'rate_duration_step': <int|None>, # Seconds
  'rate_int'?: <int>,
  'prorate_half_interval_multiplier'?: <dec>,
  # One of 'per hour', 'per use', 'per block', 'each', 'per request',
  # 'per session', 'per sample', 'per day', 'per week', 'per month'.
  'rate_unit': <str>,
  'require_account_number': <bool>,
  'site_reservation_script_id': <str|None>,
  'sku?': <str>,
  'tax_code'?: <str>,
  'tax_note'?: <str>,
  'tax_rate'?: <str>,
  'usergroup_name'?: <str>,
  'usergroup_id': <int|None>, 
}