Salesforce Sales Cloud - What causes the "API_DISABLED_FOR_ORG - The REST API is not enabled for this organization" error in Salesforce?

This error means that the Edition of Salesforce you are trying to connect to does not have access to the API. There are multiple editions of Salesforce, the group edition for example does not have access to the API. For more information on the available editions, please see Salesforce Documentation.