You need to get the API key form the bot before using the API:

• 1. Add the phone number XXX (CallMeBot Website) into your Phone Contacts. (Name it it as you wish)
• 2. Send this message `I allow callmebot to send me messages` (in english) to the new Contact created (using WhatsApp of course)
• 3. Wait until you receive the message `API Activated for your phone number. Your APIKEY is 123123` from the bot. As this is still in beta testing, the activation can take up to 2 minutes.
• 4. The WhatsApp message from the bot will contain the apikey needed to send messages using the API.
• 5. You must enter the received key above.

Detailed description how to get APIKEY could be found here.