Everything appears to be working from my end. Here are the steps.
When the insert disc 2 screen appears, click the icon that looks like a disc. This will give you 2 options. Select the option to the right that allows you to save the state responsible for switching discs .ggs, not .ggz.
Once saved, click the disc icon and switch to disc 2. Follow the instructions to reload the page, and then upload the .ggs file.
If you get stuck, try watching the video we made about it here - [SUPPORT] How to Switch PS1 Discs