Starting on Nov 2, 2020, the header parameter
x-api-key will no longer be required in every call to REST APIs. This parameter was previously used to apply usage limits against API calls for each client ID.
Calls that include this header parameter will continue to function after this date, however, the header will be ignored and call usage will be aggregated across your entire account. For example, if you use multiple client IDs in a single Cvent account then all REST API call counts and rate limits will be added together regardless of the client.
Details about usage limits can be found here https://developer-portal.cvent.com/documentation#section/Getting-started/Rate-Limits