Why can I not retrieve any new invoices even though I’ve created them in the database?

This can happen if you’ve created the invoice in your Invoice database but not set the status to Ready. Set the invoice status to Ready in your invoices database for them to be available to Pop Invoice and ready to turn into a PDF. Full instructions here

The client property does not appear in the set-up of Pop Invoice.

This could be because the client relation in your invoice database is not set up correctly. If you edit this property the “Show on NI-Clients” should be switch on, see below for an example:

If this doesn’t fix the problem then it could be that Notion is taking time to sync up with Notion. Try refreshing the page after 2 minutes and hopefully then your clients database should appear.