Hey! So the offline image mode you enabled works great for the default Mevent images because they're pre-packaged. For your own custom images, you need to do a few extra steps:
1. Put your images (PNG format only) into this folder on your server:
oxide/data/TheMevent/Images/ServerPanel/
You can create subfolders too, like oxide/data/TheMevent/Images/ServerPanel/custom/
2. In the ServerPanel editor, instead of using your Dropbox URL, set the image path to:
TheMevent/Images/ServerPanel/YOUR_IMAGE_NAME.png
Or if you used a subfolder: TheMevent/Images/ServerPanel/custom/YOUR_IMAGE_NAME.png
3. Make sure "Enable Offline Image Mode": true is set in your ServerPanel.json config
4. Reload the plugin: o.reload ServerPanel
The key thing is - you're not using URLs anymore. You're pointing to local files on the server. So forget about Dropbox, Imgur, etc. Just upload the PNGs directly to your server via FTP/file manager and reference them by path.