Billing claims to Veterans Administration can be confusing with the various regions and programs. Here is a link to a document published by the Department of Veterans Affairs that explains where to send both paper and electronic claims, and how to fill out authorization forms.
https://www.va.gov/opa/choiceact/documents/Billing_Fact_Sheetv2_508.pdf
This is a link to a video and additional information (including a video) regarding submitting claims to the VA. They also include a FAQ section for your reference.
https://www.va.gov/COMMUNITYCARE/revenue_ops/Veteran_Care_Claims.asp