I am trying to export monthly MODIS Terra Daily NDVI data from Google Earth Engine (GEE). Despite researching various platforms, including this one, I find myself at an impasse. I attempted to implement the solution  [shared by Ludmila][1] as it closely aligns with my requirements. However, I encountered the following error: 

> Image (Error) Image.reduce: Unable to reduce an image with 0 bands.

I have novice understanding of GEE.  Below is the code I'm using:

    // Set years and month
    var startYear = 2000;
    var endYear = 2023;
    var years = ee.List.sequence(startYear, endYear);
    var months = ee.List.sequence(1, 12);
    
    // Load the image collection
    var dataset = ee.ImageCollection('MODIS/MOD09GA_006_NDVI')
                      .filterDate('2000-01-01', '2023-02-01')
                      .filterBounds(ACC);
    
    // Make monthly summed mosaics
    // Loop over the years and months to get summed monthly images
    var byMonth = ee.ImageCollection.fromImages(
      years.map(function(y) {
        var yearCollection = dataset.filter(ee.Filter.calendarRange(y, y, 'year'));
        return months.map(function(m) {
          var summedImage = yearCollection.filter(ee.Filter.calendarRange(m, m, 'month'))
            .reduce(ee.Reducer.sum());
          var date = ee.Date.fromYMD(y, m, 1);
          return summedImage.set('system:time_start', date)
            .rename(date.format("MM_dd_YYYY"))
            .divide(10)  // Divide by 10 for scaling, if necessary
            .toFloat();
        });
      }).flatten());
    
    // Filter the empty ones out
    var outputMonthly = byMonth.filter(ee.Filter.listContains('system:band_names', 'constant').not())
      .sort('system:time_start').toBands();
    
    // Print the resulting mosaic
    print("Output Monthly NDVI Mosaic:", outputMonthly);
    
    // Export the data
    Export.image.toDrive({
      image: outputMonthly,
      description: "NDVI_ACC_2000-2023",
      scale: 3000,
      folder: "NDVI_ACC",
      region: ACC,
      maxPixels: 1e13  // Adjust this as needed
    });



  [1]: https://gis.stackexchange.com/questions/258344/reduce-image-collection-to-get-annual-monthly-sum-precipitation/258379