The following events pertain to Bills Company:

December 28, 2018	Bills was contacted by a customer for possible accounting and tax services.
December 30, 2018	Bills signed a formal agreement with the customer to provide accounting and tax services in 2019.
January 4, 2019	The customer paid $1,000 in advance for the services to be provided by Bills Company.
January 11, 2019	Bills provided accounting and tax services to the customer.

Using cash-basis accounting, on which date should Bills Company record revenue for the accounting and tax services?