Note, you must use the Taco Bell App + Log-in to your Account in order to achieve this offer.
Editor's Notes & Price Research
Purchase is required. Offer valid through October 19, 2015 or while supplies last. Limit 1 customer per week. Total discount capped at $10. Available at participating locations for mobile orders only. - Discombobulated
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Previous offer said Valid through 12AM PST on 10/19/15, now the offer shows a Valid through date of 12AM PST on 10/26/15. If it doesn't show up again next week for another week, it will end on Sun night 10/25 at midnight and not be valid on Mon 10/26.
Why they say valid through 10/26 when it expires at 12AM on 10/26 and therefore is not valid on 10/26 I have no idea. Someone or a lot of someones don't know the difference between 12AM and 11:59:59PM.
According to Taco Bell customer service, you need to spend over $20 to get up to $10 off.