This happens because you are still using the Community version even if you have purchased the Supporters version.
You can check this in the info section:
If you're using the Supporters Edition you should see the suffix SE beside the version number:
Instead, if you are still using the Community Edition you see the suffix CE beside the version number:
In conclusion: bibisco Supporters Edition and bibisco Community Edition are different applications, so you have to download, unzip and launch Supporters Edition as described in the link here: How to upgrade from Community to Supporters Edition.
In particular, pay attention at the name of the zip: bibisco-win32-x64-2.X.Y-SE.zip is the zip for Supporters Edition, bibisco-win32-x64-2.X.Y-CE.zip is the zip for Community Edition.