Electronic Invoice Presentment and Payment, or EIPP, is more general concept (as compared to ERS discussed earlier) that is based on electronic invoice submission. ERS uses Advance Shipping Notices (ASNs) instead of invoice. However, they share benefits: avoidance of data entry, errors and exceptions, lost invoices and vendor inquiries. Most solutions are capable of receiving invoices in CSV, XML and few other formats over EDI.

EIPP or e-Invoicing is part of the larger procure-to-pay (P2P) cycle (will be writing soon on this). A huge challenge lies in supplier on-boarding: getting suppliers to automate at their end. In the current era, supplier enablement can be hastened by hosting an internet facing portal – called Supplier Portal in sourcing jargon – that suppliers can log-on to and key-in their invoices. ‘Flipping-the-PO’ is a standard feature that saves data entry effort for the supplier, and minimizes error. On referencing the PO being invoiced, information about line items viz. description, ordered quantity & price are defaulted. This helps reduce the number of expections in automated invoice matching. Imagine this as handing over your groceries list to a baniya who converts it to a bill by stamping his name and adding prices & total (and discounts if the baniya is willing to spare)

References:
http://scm.ncsu.edu/public/facts/facs041014.html
http://www.agilent.com/oracle_supplier/downloads/ERS_supplier_guide.pdf
http://www.jpmorgan.com/tss/General/Invoice_Management/1159348844579