The search result, seen in May 2019, offered players to "create an account & play now" when they searched for ways to self-exclude from gambling.
In its defence, Casumo said it has a list of excluded terms which would prevent its ads from appearing on Google, although this particular combination of terms had not been anticipated.
The operator claimed the word "unsubscribe" was associated with being removed from a mailing list, not self-excluding from gambling itself.
Based on this defence, the ASA upheld the original complaint, despite taking into consideration the fact Casumo took immediate action upon receiving the complaint.
The ASA has ruled the advert must not appear again in the form complained of and must be responsibly targeted.
The regulatory body concluded: "Because we considered there was a strong possibility vulnerable consumers seeking to prevent exposure to gambling ads and access to gambling websites might have been served a gambling ad following a search for ‘how to unsubscribe from all gambling,’ we concluded the ad had not been responsibly targeted."