Where is the best place to convert special characters (& lt; & amp; etc.)? On the server or in the mobile app?

Question

Mobile development

Good afternoon.
I ask you for help. I am making a mobile application and in many places in the text data the API returns special characters (& lt; & amp; etc.). The API developer claims that it is necessary to remove the "load" from the server and do the replacement of characters in the application, but I think in a completely different way (he already put spokes in the wheels, and now he's just too lazy, or out of harm). Write, please, what do you think about this?