Installed file not located in designated path

Have just installed invoiceplane and trying to find way around.

Can generate quote but not create invoice.
path is looking for …/invoices/ajax/create
but the folders do not exist

The data is being parsed and is appearing in dB

Error reading is 500 internal server error

These folders should not exist.
Please check your web server error logs to find out what caused the 500 error.

Problem still continues.
Cannot execute “generate invoice” either directly or from conversion from “quote accepted”.

No error found in log. Can send log to you.

Save the logs on Hestebin or a similar service and share the link here.

And what about the web server error logs? not the InvoicePlane logs.

Please solve the issues regarding the client denied by server configuration errors with the help of this post on Stackoverflow because your web server is not configured correctly.

This is not helpful. Error codes are displayed to indicate problem. If the program does not create an invoice, there is no point in continuing.

Why is this not helpful? You posted your web server error logs which contain client denied by server configuration errors. These indicate that the web server is not properly configured to allow InvoicePlane to run and the solution is posted in link I posted.
Did you tried this?