Marketplace facilitator laws require platforms like Amazon, Walmart and Etsy to collect and remit tax on the orders they process. That removes the tax collection burden for those orders. It does not always remove the registration burden.
In states such as California, Texas and Washington, marketplace sales count toward your economic nexus threshold. Once your combined sales pass it, you must register and file for your direct sales.
On the return, the marketplace sales are reported as exempt because the facilitator collected tax. Getting this wrong in either direction creates a problem: ignore them and you miss your threshold, report them as taxable and you remit tax twice.
Reconciling by channel before each return is prepared is the reliable way to keep gross sales, deductions and net taxable sales consistent.