I checked the screen maps (https://drive.google.com/drive/folders/11vibw9j3koAxX4lAxCdePEFSkF9v1qZY) and a few videos for Dried Up Well and they all show the gold key that you need coming out of the treasure chest to the left of that gate (that you have already opened) at the same time as the blue bucket.
If that gate doesn't open as you approach it, contact Pixel Support.
On your game screen, choose the Settings wheel in the upper left corner. Write down your Player ID and then choose the Support button. Scroll all the way down to the bottom of the page until you see a list of categories. (Do not use the white text box in the center of the screen.) Choose a category and then provide your Player ID, Web-based game vs. Mobile, and problem details.
If you are using an iOS device and you do not see the category options on the SUPPORT page, you'll need to email PIXEL Support at: email@example.com . Be sure to include your Player ID.
Pixel Support responds by email. You may need to check your spam folder for their response.