The author wrote that some people would make other people do the work, taking a cut. Given, that people who work themselves at Deliveroo already struggle to get a decent salary, then yes, it is immoral.
The person with the account is providing a benefit in return for that cut, though -- the account itself and the attached phone. It's not slavery, any more than Amazon taking a cut of sales through their website is.
I fail to see how the citizen in this case is harming the non-citizen.
I fail to see how the citizen in this case is harming the non-citizen.