Corporate service buyers (CSBs) with existing CPF Submission Number (CSN) are required to register for a Contribute As You Earn (CAYE) CSN for CAYE transactions. This is because the existing CSN that CSBs have is only for the purpose of making CPF contributions to employees. A CAYE CSN will enable self-employed persons (SEPs) to identify CSBs who made CAYE contributions on their behalf. The CSN for employee transactions cannot be used for CAYE transactions, and vice versa. CSBs who need to apply for a CAYE CSN may do so via CAYE digital services.