Unable to export image to drive in Google Earth Engine

Question

I am working with Imerg data and after calculating the total rainfall from monthly averages there is an error while after I run the export.image.toDrive. The error is:

Attempted 1 time Error: Image.clipToBoundsAndScale, argument 'input': Invalid type. Expected type: Image. Actual type: ImageCollection. (Error code: 3)

Also, the projection is giving me this error:

Line 36: projection is not defined

Here is the code I am using

    //Total Rainfall
    var imerg = ee.ImageCollection("NASA/GPM_L3/IMERG_MONTHLY_V06").select('precipitation');
    
     var year = 2019;
      var startDate = ee.Date.fromYMD(year, 1, 1);
      var endDate = startDate.advance(1, 'year');
      var filtered = imerg
      .filter(ee.Filter.date(startDate, endDate));
      
    var total = function(img){
      var year = 2019;
      var startDate = ee.Date.fromYMD(year, 1, 1);
      var endDate = startDate.advance(1, 'year');
      var hoursInyear = endDate.difference(startDate, 'hours');
      return img.addBands(img.multiply(hoursInyear).rename('precip_mm_month'));
    };
    
    filtered = filtered.map(total);
    
    var palette = [ 
      '000096','0064ff', '00b4ff', '33db80', '9beb4a',
      'ffeb00', 'ffb300', 'ff6400', 'eb1e00', 'af0000'
    ];
    
    var precipitationVis = {min: 0.0, max: 10000, palette: palette};
    
    Map.addLayer(filtered, {bands:'precip_mm_month', palette:palette, min:0, max: 5000})
    print(filtered);
    
var projection = total.select('precip_mm_month').projection().getInfo();
    
    Export.image.toDrive({
      image: filtered,
      maxPixels: 1e13,
      description: 'Precipitation_2019',
      crs: projection.crs,
      crsTransform: projection.transform
      region: roi,
    });

Answer 1

As the error message states, an ImageCollection was found where an Image is needed. Specifically, Export.image.toDrive() can only be used to export single images, not image collections.

If you want to export the same (mosaiced) view that you get from Map.addLayer(), then use

Export.image.toDrive({
  image: filtered.mosaic(),
  ...

I can't help you with your additional problem because the code you have presented has different errors than you mentioned (total is not an image but a function, so total.select() fails).