Yeah, you need to build a Recruitment Radio Beacon. The one that's there is only for running the radio station.
That is admittedly unintuitive. But yeah. You need a separate recruitment beacon. Or to manually import settlers from other settlements.
You will probably be glad of it however when you either get tired of the mission spam and want ti turn off Radio freedom while still recruiting or have more settlers than you have jobs fro and want to stop recruiting without necessarily loosing radio freedom. Having separate towers lets you do that.