HTTP 406

Not acceptable

The Accept header admits none of the media types the endpoint produces, or not the one format names. Nothing was charged.

"type": "https://ohlc.io/problems/not-acceptable"

Why it happens

An Accept header such as application/xml, or application/json;q=0, on an endpoint that produces JSON.
Accept: text/csv on an endpoint without the format parameter, which produces JSON only.
format=csv with Accept: application/json, or format=json with Accept: text/csv.

Omit Accept, or send Accept: application/json (or */*).
For CSV, send format=csv or Accept: text/csv on an endpoint that lists the format parameter in the API reference.