Sharethrough is automatically added as an inventory source once a buyer has created a native creative in The Trade Desk, but users can also manually add STX to the supply list by following these steps:
1) On the Supply vendor rail, click the drop-down.
2) Type "Sharethrough" into the field
3) Click on Sharethrough in the selection window
4) Hit Save and Sharethrough will then be added as a supply vendor in your ad group.