PowerApps `not in`

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“not operator along with the custom named condition operators is not allowed”

Operator <> or NOT In. In and Exactin

For example in an Items of Gallery :

With(
    {
        userlevel_isnot_banker: First(colSession).UserLevel <> "Banker",
        isnotteamhead: First(colSession).CurrLevel <> "RO",
        isnotbanker: First(colSession).CurrLevel <> "Banker",
        ro: First(colSession).CurrTeam,
        banker: First(colSession).CurrBanker,
    },
    Filter(
        WAM_Trade_Summarizes,
        FinalDate_yyyymm in ComboBoxTradeFinalDate.SelectedItems,

        (isnotteamhead || RO_gb=ro),
        (isnotbanker || GroupBanker_gb=banker),

        (userlevel_isnot_banker || (
            Statement_prod_type_gb <> "Extra Rate" &&
            Statement_prod_type_gb <> "Management fee" &&
            Statement_prod_type_gb <> "Error"
        ))
    )
)

Use this

(
            Statement_prod_type_gb <> "Extra Rate" &&
            Statement_prod_type_gb <> "Management fee" &&
            Statement_prod_type_gb <> "Error"
        )

instead of

!(Statement_prod_type_gb in ["Extra Rate", "Management fee", "Error"])

or

Not(Statement_prod_type_gb in ["Extra Rate", "Management fee", "Error"])