TypeError: Expected cv::UMat for argument 'src'

I try to pull out the outline of the object contours from the photo, but I get an error:

Ret,thresh = cv2.threshold(img, 245,255,0)

TypeError: Expected cv::UMat for argument 'src'

Tried cv2. UMat but it didn't help, what's the problem?

if not img:
    async with plugin.session.get(photo) as response:
    img = Image.open(io.BytesIO(await response.read())).convert('L')

if not img:
    return await env.reply('К сожалению, ваше фото исчезло!')

ret,thresh = cv2.threshold(img, 245,255,0)
contours, hierarchy = cv2.findContours(thresh,cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_NONE)

tam = 0

for contorno in contours:
    if len(contorno) > tam:
        contornoGrande = contorno
        tam = len(contorno)

cv2.drawContours(img,contornoGrande.astype('int'),-1,(0,255,0),2)
cv2.waitKey()
cv2.destroyAllWindows()