Return coordinates without icao24

Hello,
I've been trying to use your API for some time now for a personnal project. I have achieved a good result, but I have a big problem. To retrieve the coordinates of an aircraft as simply as possible, I use the request "opensky-network.org/api/states/all?icao24=". It is mandatory to enter the icao24 to retrieve information from a single aircraft. Is it possible with your API to retrieve information from an in-flight aircraft with its callsign for example?
Thank you very much for everything you are doing and I hope I will find a solution, thank you for helping me!

Thank you for your answer. And for "professional", it's a mistake. I made my site for a project of which I derive no profit. It's only a project personnal but I think it's a good training.