Word Choice

I'm assuming that they already know why they will be given a lien waver.

If that assumption is wrong then ignore the following.

Attached is the finalised work order and lien waver for your invoice, or we could invoice AP on your behalf along with said lien waver.

Thank you!

Attached Are: 1. the finalized work order. 2. a lien waiver for you to provide to AP with your invoice.

Or you can also send the invoice to me and I will send it along the required documents to AP.