Im working on a GIS app that call WMS service from a Geoserver. The URL looks like this:
http://MY_SERVER_V_2_18_0/geoserver/wms/?styles=my_style&service=WMS&request=GetMap&layers=my_layer&...
As you can see I'm using plural styles on this request. This is NOT working when I use Geoserver v2.18.0, but when I use same request on Geoserver v2.17.2 I may use plural or singular style because both are accepted.
Because this problem came with a version upgrade, I need to know if I'll do right if I change my code to use singular style from now.
The keywords in the getMap URL are defined by the WMS specification and requires (and have always required) that STYLES be plural.
I don't have any instance running a service as old as 2.18 but it definitely works in 2.22.2 with STYLES (and STYLE as we are lenient in our parsing)
If you continue to have issues with STYLES in a recent GeoServer please raise a bug report.