• Go to Sigma and access your workspace.
  
• Enter the developer portal of the Zoho Books extension you're creating a connection for.
  
• Navigate to the Build section and click Connections.
  

   

• Click New Connection to create a new connection.
  

Note: Alternatively, you can use the View All option under a connection type to see all the services under that particular connection type and begin creating connections.

     

• Choose Custom Services and click Create Service.
  

   

• Provide the details of the service.
  

➤ Enter a name for the service, and the service link name will be immediately filled in.

➤ Choose the authentication type that corresponds to the authentication mechanism supported by the service for which you are building the connection. These details will be available as part of the service's API documentation. For our example, we'll use OAuth2, because Zoho Bookings supports it as an authentication mechanism.         

  

➤ The remaining fields to be configured for the service differ based on the authentication type used. In our case, the parameter type is Header, and the grant type is Authorization Code.

   

➤ Please refer to the table below for the values that need to be configured in the remaining fields.

• Finally, click the Create Service button.
  

  

• The service is created successfully. Click Create Connection to create a connection for this service.
  

• Provide the connection details, select the scope, and click Create and Connect.
  

 

• Proceed with the flow to accept the scopes and authorize the connection.
  

 

• Create custom fields for the Customers and Vendors module by selecting Preferences > Customers and Vendors > Field Customization > New Custom Field.
  

 

• Next, create a custom button and include the logic to schedule an appointment.
• Create a custom button for the Customers and Vendors module by selecting Preferences > Customers and Vendors > Custom Buttons > New.

Book meeting custom button function Deluge code - Please find code snippet as an attachment in the post

• In the above code, the Get Contacts API of Zoho Books is invoked through the InvokeURL method using the predefined connection to get the contact/customer details for whom the appointment has to be scheduled in Zoho Bookings. Refer to this post to get complete details on the parameters required to call the InvokeURL method.
  
• From the API response, the required details are fetched from which the start time (custom field data) is formatted to the way required by the Zoho Bookings API.
  
• Next, the Zoho Bookings API to get the service ID and staff ID are invoked consecutively through the InvokeURL method using the custom connection created.
  
• The Book appointment API is used to schedule the appointment using the service ID, the staff ID obtained from the Zoho Bookings API, and customer details obtained previously via the Zoho Books API.
  
• Finally, using the update contact Zoho Books API, the Zoho Bookings calendar URL is updated in the custom field created to display the calendar booking URL.