We already mix vector and text search with Elastic + Vespa. What exactly makes your thing better? Not trying to be rude, but why should we care about Yet Another Search Engine?
The tips are forcefully suggested to offset the cost of the order processing service.
These apps often take a 10%+ cut from every order. Which makes it hard to sell to a restaurant. If I pre-select 10% tip, most people will pay it making the app basically free and a no-brainer for the restaurant.
I think it should be communicated better, but this is how I've seen it work.