scale-based sizing not working

[SarahDowda]

Hello, I have recently put together a map in ArcPro and the symbols are not getting larger and smaller when zooming in and out of the map frame. In other words, when I zoom way out, all of the symbols disappear because they are so small, and I when I zoom way in, the symbols fill the entire screen because they are so large. I have "Enable scale-based sizing" checked in the Symbology pane for each layer. Is there another place it needs to be turned on for it to work?

[ISHAG_ABBASHERABDELKREEM_HASSA]

You need to check the box for Enable scale-based sizing. For example, use a larger size, such as 13 pt, for the right side and a smaller size, such as 8 pt, for the left side

[esrizarei]

the issue is the "Enable scale-based sizing" is greyed out in some occasions, when using "unique values" method

in this case, the line symbology I use could not be applied