To upload attachments you can either attach a document or, if you're using a smartphone, you can take a picture. Every submission must include at least one attachment. Depending on your circumstances, this could be receipts, signed mileage logs, signed hours/wage logs, etc. You must upload at least one attachment and you can upload as many as five.
Tip: If taking a picture, please make sure that the quality is good and that it's close enough to the document that the details are clear.