Resample of mean of ImageCollection to higher resolution

I want to resample the mean of 48 images of GPM with 10000m to MODIS in GEE. My code works perfectly for one image but the result for the mean or median of 48 images (or any number) does not correct.

The code:

var GPM = ee.ImageCollection('NASA/GPM_L3/IMERG_V06').filterDate(startdate, enddate).filterBounds(roi).select('probabilityLiquidPrecipitation').median().clip(roi);
var modis = ee.ImageCollection('MODIS/006/MOD10A1').filterDate(startdate, enddate).filterBounds(roi).first().select('NDSI').clip(roi);
var modisProjection = ee.Image(modis).projection();
var crs=modisProjection.getInfo()['crs'];
// 10,000m GPM resampled to modis 500m
var GPM_500m=GPM.resample('bicubic').reproject({'crs':modisProjection,'scale':500});
Map.addLayer(GPM_500m.clip(roi).select('probabilityLiquidPrecipitation'),{min:50, max:95,palette:palette }, 'Resampeled GPM',true); 

How can I do this?