While creating Zoho Books Contact, one can add a Contact Person to it by filling out details in the Contact Person section:
While this step passes and you have access to the Contact Person ID but in Zoho its not being created. I believe what happens is it creates the contact person but its not mapping to the customer in Zoho.
Another option is to use Create Contact Person module by passing the Customer ID to it, but it ends up with the same issue, you get the Contact Person ID for the next step but it’s not mapped to the Contact.
So when you search for the Contact next time it will not contain Contact Person in it.

