According to IRAS Audit File sample transaction entries, if there's any supply of items are classified as Customer Accounting, SRCA-S (Tax rate N/A with 0%) shall applicable to supply transaction (Eg: Cash Sales/ Customer Invoice)
Eg: Supply to Macrohard Inc. for Memory Cards with Tax Code SRCA-S, according to Customer Accounting logic, system shall not charge Output Tax (As SRCA-S with tax rate N/A, 0%) to the customer.
Referring to Requirement of you as a supplier on qualification of Customer Accounting (Page 19 on Guide on Accounting Software):
