Word Choice

This is a confusing sentence. If you're emailing this guy for a work order, why not just send him the work order? When he gets it, he'll invoice you, then you can pay him. And don't work orders usually detail the work to be done? If so, that would have been issued before the installation, so you wouldn't need to ask for it - you'd already have it.

However, if you want an answer to your question:

Please invoice us for the siding installation so we can pay you.

Hi Mame,

Thank you for your response. This circumstance was different than our usual practice of sending a work order first before receiving an invoice.