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The authentication Web API call that should be performed is POST authentication/web_api_key/token (based on HTTP Basic Auth)
Web API Key Method Example
Using Fields Set
CRM.COM Web APIs offer the possibility to select the fields that will be retrieved from each API method by specifying the "fields_set" input parameter. Using such parameter provides the ability to filter the response object and retrieve only the fields that will be used for the implementation. If "fields_set" is not specified, then all fields will be retrieved
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