A CSP is an agent certified under the Streamlined Sales and Use Tax Agreement to perform all the seller's sales and use tax functions, other than the seller's obligation to remit tax on its own purchases. A CSP is designed to allow a business to outsource most of its sales tax administration responsibilities. CSP services are provided free to sellers in the Streamlined Member states in which the seller is a "volunteer seller" as defined in Section D.2. of the CSP contract. More detail
A CAS is software certified under the Streamlined Sales and Use Tax Agreement that is designed for a seller that wants to use certified tax calculation software but keep the responsibility for filing returns and remitting the tax in-house. More detail
Before you register contact the CSP and/or review the CSPs website to determine which CSP will work best for you. The CSP will work with you to determine when the CSP will begin providing services to your company. The CSP will register your company when you and the CSP agree the CSP will begin providing CSP services.
Note: If you are required to collect and remit taxes in a state before the date the CSP will begin providing services, you can register through the Streamlined Sales Tax Registration System (SSTRS) at anytime. The CSP will update your account when their services begin. You are responsible for collecting the tax and filing the returns until the CSP begins providing services to you.
If your CSP stops providing services or you choose to stop using a CSP, you will still be registered to collect and remit sales tax. You may either report the sales tax directly to each state using their online filing systems or you may choose to contract with a different CSP. You are responsible for filing returns for any time period you are not under contract with a CSP.