Skylio - CRM Connector requires API Field Name of a Custom Field of Zoho Books to Sync the data on to it.
You need to first create custom fields on your Zoho Books then get the API Name of the created field.
Follow the below steps to create custom fields.
1. First login to your Zoho Books then Go to Settings -> Preferences.
2. Chose Module for Custom Field (e.g. Sales Orders) then go to Field Customization -> New Custom Field.
3. Enter your field name with other details and Save.
4. A custom field is created. Now go click on the created field.
5. You will find the API Field Name at the bottom of the page.
Now copy the API Field Name and paste it on the Skylio - CRM Connector page to sync data on to it.