Which of the following are the invoice efficiency challenges?

Missed discounts are indeed a significant challenge related to invoice efficiency. In the procurement process, timely invoice processing is crucial to capitalize on early payment discounts offered by suppliers. When invoices are delayed, placed in incorrect queues, or not monitored effectively, organizations often miss out on these discounts, which can cumulatively lead to substantial financial losses. This inefficiency reflects the organization's inability to optimize cash flow and supplier relationships, underlining the necessity for automated invoice processing solutions.

The other options present scenarios that do not directly align with challenges regarding invoice efficiency. For example, increased supplier discounts and enhanced cash flow would typically be positive outcomes of an efficient invoicing process. A standardized approval process, while beneficial for consistency, is not inherently a challenge; it can actually facilitate efficiency if implemented correctly.