You might get error "500 Server Internal Error" when I try to login the web interface. It occurs when the flash storage is full.
Please try of use SSH console to check which files.
1) Try to input command: df to see which path exists 100% usage or close to 100%.
2) Then enter the path which has 100% usage. Input command: du * -sk to see if any file occupy the storage with abnormal size.
3) Try to use rm command to delete the unnecessary files.
Caution, If you don't know if it is safe to delete, please seek support from Yeastar team.