According to the Associated Press, those colorful new $20 bills do not work well with automated payment machines.
Officials at the Bureau of Engraving and Printing are frustrated. They tried to avoid a repeat of the difficulties that occurred with the rollout of the 1998 redesign of the $20 bill.
During the last year, the bureau reached out to the vending machine industry, transit authorities, and the gambling industry to help them prepare for the colorful new bills. Unfortunately, nobody thought about the automated payment machines in self-service checkout counters before the new currency was in circulation.
This is merely an inconvenience rather than a serious problem. Signs are posted at some automated payment machines advising customers to exchange the colorful new bills for old green ones. The problem can be solved by software or hardware upgrades to the automatic payment machines.