```python
def hex_groups(values: list, width: int) -> str:
    if not isinstance(values, list):
        raise ValueError("The first argument must be a list.")
    if not all(isinstance(x, int) and 0 <= x <= 255 for x in values):
        raise ValueError("All elements in the list must be integers from 0 to 255.")
    if not isinstance(width, int) or width <= 0:
        raise ValueError("The width must be a positive integer.")

    hex_values = [f"{byte:02x}" for byte in values]
    return ' '.join(hex_values)
```