If condition in postgres function

CREATE FUNCTION public.feerange (txamount decimal,amount decimal,latefeemax decimal)
    RETURNS INTEGER $feerange$
    DECLARE total INTEGER;
    DECLARE amountsum DECIMAL;
    BEGIN
    
    amountsum= amount + latefeemax;
    if txamount <= amountsum AND txamount >= amount
        THEN total=1
        else
           total=0
     RETURN total
    
    END; 
    $feerange $ LANGUAGE plpgsql;

while creating this function I'm getting an error of if condition

but I don't think there anything wrong.

the error is I'm getting is

/* ERROR: syntax error at or near "if" LINE 1: if txamount <= amountsum AND txamount >= amount

What is wrong with this? Help me to do this! Thank you !!