'Opt-in,' a verb equivalent, is the act of agreeing to or asking for a given product or subscription, like a newsletter or rewards system.
OPTI - OPTIC - OPTICS - OPTIMISM - OPTIMUS - OPTINT - OPTIONALIZE - OPTIONS - OPTIR - OPTITEAM
"OPTIN." Abbreviations.com. STANDS4 LLC, 2015. Web. 8 Oct. 2015. <http://www.abbreviations.com/OPTIN>.