I'm working with the light switch server example and nRFMeshProvision example project for iOS.
How do you send arbitrary data to a board? I understand the provisioning process and turning the light on/off on the board but we also want to send arbitrary data like strings from the iOS device to the board that would be saved to flash memory on the board.
Have a look at this thread, it includes a custom simple_message model example that will let you send a string over the mesh network. It is made for Mesh SDK v1.0.0 but I suggest you to use the example application as a reference/guidance on how you can make a custom model for Mesh SDK 4.0.0, that let you send a string.
Other relevant links:
Creating new models
Receiving simple message mesh
Hope this helps.