Here is some confusion for us. We have both CRM and Books. Here is what we see with Books integrated to CRM:
CRM / Potential:
-sales order
-invoices
-estimates/quotes
-purchase orders
Zoho Books (as shown as a tab in CRM)
-sales order
-invoice
-purchase order
But those two above do not sync up! An "invoice" created in the CRM (and attached to a Potential for easy reference) does not show up in Zoho Books. You have to create it IN Zoho Books if you want to e-mail to customers with a billing method attached (PayPal, etc.).
My suggestion: If a user has set up an integration set up between Books and CRM, then allow a choice to "convert" all/any/specific records over to the Books side of the account and allow us an integrated experience. Either that or just have all record types sync up between systems.
Case in point: I have Price Books set up in the CRM based on % discount based on quantity ordered...works great. But I cannot create an invoice with a credit card payment link in it, because I cannot convert that CRM invoice into a Books invoice. And the Books "Price list" feature is nowhere near as advanced as the CRM one. SO, I have to manually type-in all the info into Books, even though it is completely filled out in the CRM.