How can I tell if my Walk in Run is a Mk2 or Mk3?

The easiest way to tell is to look at the size of the mesh panels.
On the Walk in Run Mk2, each mesh panel is a single 90cm x 90cm panel. On the Walk in Run Mk3, each 90cm x 90cm section is made from two smaller half panels, clipped together. You will see a line of clips where the two halves join.
If you purchased your Walk in Run before June 2023, it is likely a Walk in Run Mk2.
Mk3 mesh panels and extensions are compatible with the Mk2 Walk in Run, but they will look slightly different because of the split panels.