What you need to do is the following:
- Have both IAPs connected on the same VLAN so they can build a cluster.
- Once the cluster is build you should be able to disconnect the IAP you are planning to use as the Mesh point.
- If you only provide power to that IAP (NO NETWORK) then it should be able to build a mesh link automatically if the mesh point is able to build the link with the Mesh portal (IAP with Network connectivity)