Here are some error messages that you might receive:
cURL error 28: Operation timed out after 5000 milliseconds with 0 bytes received
This error message will be returned when there is a problem communicating with the ActiveCampaign servers.
You will see additional information with this error, such as, Unable to add contact to list from ActiveCampaign: Array ( [email] => firstname.lastname@example.org [p] => 2 [status] => 1 ).
Please contact ActiveCampaign support and inform them that you are getting this error while trying to access ActiveCampaign via the API version 1.
Unable to [SOMETHING]: You are not authorized to access this file
ActiveCampaign does not recognize your API URL and API Key combination. Please verify that you have entered the proper values for these two variables. If you entered the correct data and it is still not working, please contact ActiveCampaign support and explain that your API data is not working.