The Copper API is returning a 10/17/2023 close date. It's either a Copper bug or Copper configuration (time zone) issue .
You have an Opportunity (Id 30303531) that has a close date of 10/18/2023 in Copper however, the API returns a close date of 10/17/2023 for the opportunity.
We checked the Copper API webhook log (for our app) and saw that the Copper API returned a close_date = "10/17/2023" for the opportunity.
We re-checked the Copper API directly using Postman to compare with our logs and still see "10/17/2023" in the API response.
There is no information about close_date's timezone in Copper API documentation. That may be a possible explanation.