Smooth transition on bezier curves

Hello out there
how can I achieve a smooth transition to a thickest part in the middle… without that " sharp ring" in the middle

There are two ways to do this. The first way is to go to the Active Spline panel and change the Radius interpolation type from “Linear” to “Ease” or “B-spline”. The second way is to go to the Geometry panel and use a separate Taper Object to define the radius of your crescent moon instead.