Sends the job's contact a link to a page where they can view the invoice and, when online payment is available, pay it. Use it to collect a deposit or final payment without the homeowner needing an account.

• The link goes by text message if the contact has a phone number and has opted in to texts, and by email if they have an email address.
• The wording adapts to the invoice: a payment request when it can be paid online (status sent or overdue with a balance due), a financing message when payment_type is financing, and a view-only message otherwise.
• This endpoint does not change the invoice's status. Messages are sent in the background, so a 200 means they were queued.
• The token's role must be able to view all company records, or the token's user must have created the invoice. The token needs the write scope.