Zoho People billing into Zoho Books - ERROR: Please enter a suitable VAT treatment

Zoho People billing into Zoho Books - ERROR: Please enter a suitable VAT treatment

Hi everyone,
When I create a bill in Zoho People and try and send it as an invoice to Zoho Books I get the message from Zoho books "Please enter a suitabel VAT treatment".

I am pretty sure I know what this means in terms of where either my business or my client's is regsieterd for VAT but i cannot find where i need to make that change.

Can anyone help?

M