proof-of-purchase

[ proof-uh v-pur-chuh s ]
/ ˈpruf əvˈpɜr tʃəs /

noun, plural proofs-of-pur·chase.

a sales slip, label, box top, or other item associated with a product that is presentable as evidence of actual purchase, as for claiming a refund or rebate.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019