If you're receiving an error while trying to sync your Salesforce Account to your Sales Navigator account, there might be an API enablement issue. Salesforce only supports API access for the Enterprise, Unlimited, Developer, or Performance edition of Salesforce. Salesforce does not support the API package for Contact edition or Group edition. API access can be purchased for Professional edition from Salesforce.

Take a look at what Salesforce editions have API access.

You'll need to contact your Salesforce admin who can reach out to Salesforce to obtain this API key in order to successfully integrate your accounts.