I’m trying to protect my invoice page with a .htaccess password. Unfortunately I always get a 500 internal server error. I tried different passwords, e.g. without special characters, but that didn’t help.
I don’t have a solid solution, but I would suggest you try to password protect any other directory on the server with plain html files in it, just to make sure the error 500 is not related to InvoicePlane. If that too is throwing the same error, then it’s not a problem with InvoicePlane.
Last but not least… Is the /path/to/my/.htpasswd correct (based on server root) ? Does the process of the web server have access to this file (permissions) ?