It seems there may have been a typo in the coordinates you've provided for the octagon. The first vertex is clearly labeled as \((-3.4, 6)\), but the second vertex appears to have an extra value: \((-3, 4, 2.6)\). Typically, a vertex in a two-dimensional coordinate plane should have only two values (x, y).
If you can clarify the coordinates of the octagon or provide more information, I would be happy to help you answer questions related to it!