Whether or not you can use APIs, JavaScript/CSS customization, plug-ins, and integration services depends on your license plan.
For details on the available license plans, refer to the product website below.
Pricing (Only available in Japanese)

Customer support is available for inquiries regarding API specifications. To send an inquiry, use the email inquiry form. For information on how to contact Customer Support, refer to the following page.
Contacting Customer Support

Customer support is not available for inquiries regarding customization using APIs, JavaScript or CSS.

Customization requires a knowledge of programming. If you want to develop your own customization, please refer to the following websites.

• cybozu developer network (Only available in Japanese)
  This website provides essential information for customization, including API documentation and sample code.
• cybozu developer community (Only available in Japanese)
  This is an online community where users can discuss customization and customization-related issues.

Customization can also be requested from partners.
Search for a partner that's right for your operation from Cybozu Partner Network and consult with them. If you're not sure which partner to consult, use the Partner Selection Support Service.

• Cybozu Partner Network (Only available in Japanese)
• Partner selection support service (Only available in Japanese)

Customer support is not available for inquiries about plug-ins or integration services.

Please search for the plug-in or integration service that you're looking for on the product website, then contact the provider for assistance.
Plug-ins and integration services (Only available in Japanese)