An ERP (Enterprise Resource Planning software) is a business process management software generally used by finance and accounting departments. Most large corporates use an ERP system to support their procurement process; often, ERP systems will have a procurement add-on module. However, these are often not enough and can't handle all procurement functions well.
ERPs are often expensive and complex. They require time to be implemented into a company's on-premises systems, and then require employees to be trained to use them.
On the other hand, e-procurement systems are explicitly designed as a one-stop-shop to handle all your procurement needs. The best ones are intuitive and easy-to-use and do not require any training. Because they are cloud-based, e-procurement systems can be implemented quickly and provide a quick return on the investment.
As comprehensive as ERPs are, the process still includes a manual data entry component, where quotations are manually requisitioned from the market and then entered into the system. Comparison statements are also usually manually made on excel and approvals obtained offline, before the final selected price is entered into the system for approval and purchase order creation.
E-procurement solutions automate this process. They serve as fully independent, standalone procure-to-pay systems where requisitions can be created, approved, and submitted to vendors, and subsequently quotations can be received, compared, and approved for purchase orders to be issued.
Vendors, too, can either enter their quotations into the specified form fields, or they can respond to the email notification with a quotation attached as a document or a direct message through email. The advantage of having all the documents directly submitted to the system allows for a greater level of transparency and integrity.