When eBay and PayPal split up on Friday, they will face different challenges than they did as a combined company. E-commerce company eBay first said in September 2014 it would split off its payments unit PayPal, in order to focus the two companies on growing profits individually. Investors, including activist Carl Icahn, had lobbied for the movie. Though the split happens Friday, PayPal starts trading on the Nasdaq under the "PYPL" ticker on Monday, while San Jose, California-based eBay will keep trading under the "EBAY" symbol.As separate units, eBay faces stiff competition from Amazon and other online retailers that have gained market share from traditional brick-and-mortar stores. On the other hand, online payment system PayPal, which had long been eBay's fastest-growing segment, will have to compete with mobile wallets like Apple and Android Pay and online payment offerings from Chinese e-commerce retailer Alibaba and other retailers.