During the 1920s, how did credit card debt play a role in causing the great depression? not enough cash was floating around. people could not pay off their bills. interest rates were not high enough. there was no longer a need for banks.

The answer is "People could not pay off their bills". 

In the 1920s, individuals would frequently purchase things using a credit, without much worry about how they would pay it back. At the point when the Great Depression began, many individuals were at that point owing debtors and could never again pay back what they owed. This prompted the crumple of numerous business. 
Many stores and organizations presented credit to customers, which enabled them to purchase things like autos, radios, coolers and so forth with just a little initial installment and afterward pay the rest back after some time. At the point when the share trading system smashed in 1929 and thousands of individuals were tossed out of work, they couldn't pay off their debt which at last made stores go bankrupt and banks to come up short, tossing more individuals out of work.