When anyone uses MySalesData for Salesforce Google Sheets Add-on one can face an error:
The rest API is not enabled for this organization
This happen because by default in MySalesData for Salesforce enabled REST API. This a modern API is available only for Salesforce users who have an Enterprise or Unlimited edition of Salesforce. If you don’t have that edition you have to use SOAP API that is available for all types of Salesforce editions.