Hey guys, does anyone know if it is possible to target the expense subtab on a vendor bill with a workflow?

No @Geoff Hiltgen sorry it is not possible. The only option is the Items subtab. If you can make an Item record that has the same expense account as what you would add on the expenses tab you might be able to use that Item and use the Items sublist in a workflow

@AI1 Dang, that’s a bummer. Well thanks for the info and suggestion!