Your JSON file should be an array of bounding box objects with the following structure:

[
  {
    "offset": [z, y, x],
    "shape": [depth, height, width]
  },
  {
    "offset": [z, y, x],
    "shape": [depth, height, width]
  }
]

Example:

[
  {
    "offset": [50915, 22126, 18411],
    "shape": [22787, 11225, 12566]
  },
  {
    "offset": [100000, 50000, 30000],
    "shape": [20000, 15000, 10000]
  }
]

Notes:
• Coordinates are in nanometers
• Order is always [z, y, x]
• Shape represents the size in each dimension