cURL API - can't figure out export readings
I have a SMETS2 meter. I get solar export payments from my provider (Octopus).
I've set up the Glowmarkt app with DCC integration (I don't have any hardware from them).
I can make API calls using
curl -X GET -H "Content-Type: application/json" -H "token:..." -H "applicationId:..." "https://api.glowmarkt.com/api/v0-1/resource/.../readings?from=2022-09-10T00:00:00&to=2022-09-10T23:59:59&period=PT1H&offset=-60&function=sum" | jq
Which returns hourly readings as expected:
[ 1662786000, 0.257 ],
But, when the sun rises, the reading just shows zero.
I've tried functions of both sum and avg - are there any others? - but still nothing.
I've had a look through the forum, but I can't see anything about getting export readings through cURL. What blindingly obvious thing am I missing?