CDON defines a Missing Shipment as "A package the customer feels they have not received". A customer can only report an item Missing once the delivery window has expired. So It's important to have an accurate delivery window for your products.
Customer reporting a Missing Shipment within the delivery window
When a customer reports a Missing Shipment, an automatic check is performed for the delivery time. If the delivery window has not yet expired, the customer cannot create an errand.
I have a valid tracking number
You can only decline an errand for a Missing Shipment if you have a fully traceable tracking number* which shows the article has been fetched, or is available at a pickup location near the customer. Otherwise, the customer should be offered a new shipment, with a valid tracking number attached to the email, or be refunded.
If the tracking number is valid, share the tracking link with the customer and put the errand's status as Errand rejected in Reclaimit.
*Please note Varubrev is not approved as fully traceable.
The customer's address is wrong
If you suspect the customer has provided an erroneous address, verify the address by asking the customer in their errand. When the customer replies with the correct address, you can send a new item there.
Make sure your shipments include your return address. That way the first, incorrect, shipment will be returned to you so that it can be re-sold.