Woocommerce ZOHO integration debugging how to fix: Function error (source_validate): [DESTINATION FIELD | email] [SOURCE FIELD | Email]: <string(0): ""> - The source field "Email" has invalid value.
In this case the above error is caused by empty an email source input from Zoho CRM
Because the field was set to type email, there would be a validation for the input email fields(it has to be firstname.lastname@example.org format).
If the email field doesn't always exist, what we can do is set the email to 'string' then it will skip the validation. (This will cause failing to create customer in Woo as email is required in WooCommerce)
If you are only looking for updates from woo commerce to Zoho, then they should change direction from "both" to "to slave". (email should always exist in woo)