Void an invoice
Servicebay doesn't have a separate "void" status for invoices, so there's no way to mark one cancelled while keeping it on record. If you created an invoice in error, the way to deal with it is to delete it, which removes it permanently.
Open the invoice
Go to the Invoices tab and open the invoice you need to cancel.
Open the actions menu
Tap the ⋮ menu in the top right of the invoice (or the trash icon directly, in landscape).
Choose Delete
Select Delete. You'll be asked to confirm: "Are you sure you want to permanently delete this invoice?"
Confirm the deletion
Tap Delete to confirm. This is permanent: the invoice and its share link are removed and can't be recovered, and its payment history is no longer accessible from the app.
Let your customer know
If the invoice was already emailed, send the customer a quick note so they know not to pay it, since the link they were sent stops working the moment you delete it.
Tips
Deleting doesn't renumber or reuse invoice numbers, so your invoice numbering stays sequential even after a deletion. If the invoice has already been partly or fully paid, check with your bookkeeper before deleting it, since once it's gone you and your customer lose access to the invoice and its payment history, with no audit trail left behind.