Hey, Vault Hunters!
We’re aware there's an issue on PC with the player's UI when selling items at a vending machine. The good news is that there is a workaround that you can use in the meantime while the development team works on a fix for this.
While in the selling menu, you can use the directional arrows on your keyboard to navigate through your items. You can also use the W, A, S, and D keys the same way you would use the arrow keys to view your items!
Hopefully, that helps a bit while the development team works on fixing this issue. If you have any additional questions or technical issues, you can always create a Support ticket to reach out to us!
Take care, Vault Hunters!