I wonder what happens if a customer tips more than what Instacart would have paid? I read through the blog post on Medium and the article, but couldn't find an

I wonder what happens if a customer tips more than what Instacart would have paid? I read through the blog post on Medium and the article, but couldn't find any case where the customer had tipped more. Is $0.80 the minimum payment they will make, or will it decrease further – negative?