The date/time format is in an ISO8601 encoded date time. For example, in the request:
curl -H "Authorization: Bearer ${access_token}" \ "https://api.truelayer.com/data/v1/accounts/${account_id}/transactions?from=${from}&to=${to}"
The datetime should be formatted like this:
2018-02-18T00:00:00
If you need more information
Check out our comprehensive API documentation with more details.