403 error when creating New Users

Hello everyone, I recently installed InvoicePlane and everything went very well until I got in to settings and tried to create another user.

When I go to User Accounts > New > Save: I get a 403 error saying:
‘You don’t have permission to access /invoices/index.php/users/form/1 on this server.’

The console has the error “Failed to load resource: the server responded with a status of 403 (Forbidden)”

I checked the logs in application/logs and saw nothing relating to users or permissions.

I can create new inventory, quotes, invoices and clients, and was able to create the initial user with no problem. This is the only thing that messes up.

Any help would be greatly appreciated!