When you receive a dropshipping order, the Retailer will pay your commission and the cost of shipping via PayPal. You will receive that payment directly in your PayPal account.
If you are a Shopify user, please note that shipping payment will not be included in your Shopify account but will be shown in your Paypal account. Please check your Paypal to see that the shipping was included in the payment.
You will always receive payment for a product before you need to send the product to a customer.