Answer:
If the toilet flapper gets stuck in the open position, it may be due to calcium or other water deposits. You can try submerging the affected part in a 50-50 mixture of water and white distilled vinegar to break down the deposits. Alternatively, soak a paper towel in vinegar, wrap it around the post, and leave it to sit.
If the issue persists after these suggestions, we would suggest replacing the flush valve as it could be an issue with the flapper or the posts.