Why do I get a "wl: error -20" when setting 40MHz channels in the 2.4GHz band for Sterling-LWB or -LWB5 with the wl tool?

Despite the fact that setting this testcase is described in the Sterling-LWB/LWB5 certification guide, neither of the two modules support 40MHz wider channels in the 2.4GHz band.

Please disregard that test case on page 13 in Sterling-LWB/LWB5 certification guide  version 1.2 or older.

Only 20MHz channels are supported in the 2.4GHz band by these two modules.