Yes, it is possible to record additional time to a Fixed Price task that has been invoiced.
Have a look at similar frequently asked questions or visit our FAQs page for more information
Is there a way I can send an invoice to two email addresses in one go?
How do I make a treatment plan for a patient?
Can you resend my activation email for my trial?
What is the best way to change my Xero invoice settings?
Can TidyStock show customers' Purchase Order Numbers on the sales tab?