If you need to email the customer their order invoice, you can do this from SellerExpress. If you find the order and click on that to bring up the order details below you should see there is a send email button.
Once you click the send email button you will see the screen below. You will need to tick the attach invoice option which will generate a URL in the text box to send to the customer. The customer will then need their marketplace Order ID to be able to view the invoice. As you can also see from the screenshot the system will also automatically add the marketplace Order ID for you as well.
If you want information to display in different lines on the email you will need to use HTML to add line breaks as shown in the image below. To take a new line in HTML you need to simply add <br> at the start of the line. You do not have to add the code for the line break on the first line.
If you do not use these the information will display to the customer in one line.
You can also test how the email will be displayed by emailing it to yourself first of all before sending to the customer.