The general revenue sourcing rules are in Article 4 of the Progress Report on Amount A of Pillar One. Schedule E of the Progress Report provides the detailed revenue sourcing rules which include the reliable indicators that can be used to source revenue.
Once revenue is sourced, the profit reallocation calculation can then be undertaken to determine the amount of profits allocated to market jurisdictions.
Whilst the general revenue sourcing rules provide the high-level rule for where revenue is determined as arising, the reliable indicators include the detail as to what multinationals can use to actually apply that rule.
For instance, the general sourcing rule may state that revenue is sourced where the place of use is. The reliable indicators may then state this can be the location of the customer based on their address or IP address.
For a detailed analysis of the Reliable Indicators under Amount A of Pillar One, see Reliable Indicators and Pillar One.