Error creating an Invoice in Zoho Projects

Error creating an Invoice in Zoho Projects

I'm trying to create an invoice for the first time in Zoho Projects and am getting a strange error message that I don't understand. It says:

"Sales order disables. Please, Enable Sales Order to access sales Order related settings." 

I have my Zoho Projects account integrated with my Zoho Invoices account.

Help!

Thank you!