Under the new rules the marketplaces are responsible for collecting and reporting VAT on B2C sales when they facilitate import of goods below EUR 150.
For any other transactions (eg imports above EUR 150, sales of goods within the EU or movement of stock between warehouses) you remain responsible for collecting and reporting of VAT.
You can use the IOSS or OSS schemes to simplify your obligations for B2C sales or use standard VAT registrations and file VAT returns under these registrations.
More information about how the new rules apply to specific transactions can be found at: https://taxually.com/e-commerce/