Python if statement: Unindent does not match any outer indentation level

I have the following Python code

def reward_function(params):
        import math
        # Read input variables
        waypoints = params['waypoints']
        closest_waypoints = params['closest_waypoints']
        heading = params['heading']
        # Initialize the reward with typical value 
        reward = 1.0
        # Calculate the direction of the center line based on the closest waypoints
        next_point = waypoints[closest_waypoints[1]]
        prev_point = waypoints[closest_waypoints[0]]
        # Calculate the direction in radius, arctan2(dy, dx), the result is (-pi, pi) in radians
        track_direction = math.atan2(next_point[1] - prev_point[1], next_point[0] - prev_point[0]) 
        # Convert to degree
        track_direction = math.degrees(track_direction)
        # Calculate the difference between the track direction and the heading direction of the car
        direction_diff = abs(track_direction - heading)
    if direction_diff > 180: # This line gives me the ERROR
        direction_diff = 360 - direction_diff
        # Penalize the reward if the difference is too large
        DIRECTION_THRESHOLD = 10.0
        if direction_diff > DIRECTION_THRESHOLD:
        reward *= 0.5
        return reward

I have tried a few different editors, but unable to fix this indentation issue. Any pointers are very welcome.