What happens when there is existing credit on the guest /company profile?

elina will use any existing credit on an account to pay any invoices that can be paid in full once the invoice is due. 
Eg: If you have £50 credit on the account and the invoice is for £100. elina will not touch with credit BUT if you have an invoice of £50 then elina will use the credit on the account.   
If you process any invoices, elina will use account credit first and use the remaining balance by your preferred payment method.