Import payments shows error - Invoice Number: Please specify the payment received for this invoice.

Import payments shows error - Invoice Number: Please specify the payment received for this invoice.

I am just starting up Zoho Books. I have successfully imported contacts, projects, timesheets and invoices, but I'm stuck on importing the payments received for those invoices.
I am using the .csv template on the website, dates and numbers are all formatted correctly.
No luck importing any of the payments.

Any ideas?
Do I need to set up anything else before I import?

Thanks!