curl --request POST \
  --url https://api.globalwebindex.com/v3/query/audience_wave_counts \
  --header 'Content-Type: application/json' \
  --data '
{
  "expression": {},
  "locations": [
    "s2_1",
    "s2_44"
  ],
  "waves": [
    "q1_2019",
    "q2_2019",
    "q3_2019",
    "q4_2019"
  ]
}
'

{
  "base_size": 123,
  "base_sample": 123,
  "audience_sample": 123,
  "audience_size": 123,
  "audience_percentage": 123,
  "per_wave_count": [
    {
      "code": "q2_2019",
      "name": "Q2 2019",
      "sample": 10,
      "percentage": 0.3
    }
  ]
}