English: Your Mailgun Private API key. For more information on where to find your Private API key, see <a target="_blank" href="https://help.mailgun.com/hc/en-us/articles/203380100-Where-Can-I-Find-My-API-Key-and-SMTP-Credentials-">here</a>
Dutch: Je Mailgun privé API sleutel. Zie <a target="_blank" href="https://help.mailgun.com/hc/en-us/articles/203380100-Where-Can-I-Find-My-API-Key-and-SMTP-Credentials-">hier</a>