Before you are able to start sending Pallet shipments with TNT via Shiptheory, you will need to have discussed this with your TNT account manager and had the service enabled on your TNT account. When discussing this with you, they will assess whether your account needs to be enabled to allow longer shipment package dimensions and heavier weights. If you do not do this, TNT might not send the appropriate vehicle to collect your shipments and you could be billed incorrectly.
Once you have had pallet services enabled on your account, we recommend you read the following article on how to set pallet dimensions to use for your shipments: TNT Formats Explained
For any other questions, just get in contact with the Shiptheory support team!