You may have double verts. On the Bevel Modifier, Clamp Overlap is enabled. This stops the bevel from overlapping the next verts along the edges. Uncheck this and try again. If it now bevels but gives a horrible looking mesh overlap, undo the bevel (CTRL+Z), Press A to select all, Press M and select ByDistance, This will remove any double verts.
Re-enable Clamp Overlap and try the Bevel again.
