Stuck on Stage 80 for ages

I was stuck on stage 80 for 4-5 days. Almost gave up on the hidden quest, but luckily I passed it suddenly. After completing the remaining 20 stages in half a day, I got the reward. For those who are playing, I recommend checking the bonus rewards when clearing stages and not spending gold too easily. Otherwise, when a stage is really hard to pass, you'll run out of gold and won't be able to get out of it.