One of the things that differentiates independent contractors from employees is that the IC invoices the client. Employees don't invoice their employers.
While some companies will pay based on the report, others are not out of line in requesting an invoice. Perhaps they have been audited in the past about whether their workers are IC's or employees and are trying to make sure they can defend the IC status if audited.
Issuing an invoice if needed is part of being in business for yourself. I signed up for the IC Pro thing and it invoices many companies for me.
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I pray it does not occur that the last thing I did before I died was vacuum the house or eat broccoli.