Time Intelligence Invoice Date & Invoice Pay Date

You've got 2 date fields in the main table so you have to either disconnect your Date table from it or have 2 relationships between the tables out of which one will be inactive and activated with USERELATIONSHIP within a measure. Or, you could have 2 different Date tables, one for invoice date and the other one for invoice payment day. What you choose depends on what you want to calculate in your model. If you want to be able to show on one time axis the number of invoices raised and paid, then you should opt for one Date table with either no connection to the main table or 2 connections (one inactive).