USA – Must you include an invoice copy in your shipment if you are the seller and buyer has same info in their Amazon account?

I was just thinking about doing product fulfillment myself on a smaller item and it would be great to save paper printouts that people don’t like when they get a shipment on low cost items…

I am in the USA and was thinking about literally just putting a 5 x 5 x 1″ product in a bubble wrap envelope and shipping it out to customers… I am interested in was of fulfillment and not wasting paper.

What risk might be involved with this?

I intend to start out on Amazon selling and move forward from there…. Eventually turning over to a fulfillment center(likely not FBA) after things get stable enough