Final answer:
The truth of the promotional offer regarding the addition of a sidecar of Cointreau or Grand Marnier to a margarita for a specific price depends on the particular establishment's pricing and cannot be universally confirmed.
Step-by-step explanation:
The statement 'Add a Sidecar Of Cointreau or Grand Marnier to any margarita for just 1.99?' is a promotional offer that may be true or false depending on the establishment. A sidecar is a small serving of alcohol that is meant to complement a drink, in this case, a margarita. As a tutor, I do not have information about specific promotions of bars or restaurants, meaning I cannot confirm the accuracy of this offer. Instead, this question seems to pertain to business operations, specifically within the service or hospitality industry, where add-ons and upgrades to beverages can vary in pricing.