Benepass does not require you to submit receipts for your HSA if you use your HSA card directly at an eligible merchant. If you use your white Benepass card or submit an expense, however, you will be asked to provide a receipt.
That being said, it is a best practice to save your receipts for tax purposes to prove that you used HSA funds on qualified healthcare expenses. On the off chance you are audited, you may be required to provide substantiation of your HSA spending. If you are not able to provide substantiation, such as a receipt or medical invoice, then you may be taxed on it.