Not booking through a travel agency

When I put Oman in the nationality box, I got a pop up which said In order to process the visa, I need to send to visa@vietnam-evisa.org

"Business invitation letter or booking tour voucher of travel agency in Vietnam

The Vietnam Immigration Department will check your status within 2 days. Then we will inform the result for you. If your visa application is approved, we will send you the notification including the visa letter."


My husband (who is German) and I will be travelling only as tourists in Hanoi and Da Nang and will not be using any travel agency. Can I still apply for the visa and send the other documents (passport, flight and hotel booking) to the email?