Pygame mask collisions not detected

Question

I know there are several questions about collisions but I can't understand how to do it, the mask of the two objects are created correctly (if I show the two rects, they are in the right place) I think I'm having troubles with the offset, I know that in the offset we have to put the distance between the top left corners of the images ex:

offset = (character_x - collisionrect_x), (charcater_y - collisionrect_y)

and I did it but:

• I can't get how the offset works, I searched online but I didn't find anything clear 2
• even if I put the right values, I always return no collisions.

Here is the function to detect collisions (simplified):

#inizialize collisions with room
collisionsroom1 = pygame.transform.scale(originalcollisionsroom1, (ROOTwidth/2.3, ROOTheight))

def collision_room1():
    #room 1 collision
    collisionsroom1_mask = pygame.mask.from_surface(collisionsroom1)

    #character hitbox
    characterhitbox_width = characterhitbox.get_width()
    characterhitbox_height = characterhitbox.get_height()
    characterhitbox_mask = pygame.mask.from_surface(characterhitbox)

    offset = ((playermovement.playertopx + sprite_width/2 - characterhitbox_width/2.2) - (ROOTwidth/2 - room1_width/2), (playermovement.playertopy + sprite_height/2 - characterhitbox_height/2.2))

    collision = characterhitbox_mask.overlap(collisionsroom1_mask, offset)

the values in the offset are correct, if I blit the two collisions in that position they are correct, I did (character_x - collisionrect_x), (charcater_y - collisionrect_y)

I return collision only if I go in the top - left, I don't know that to do