need correct format for esriGeometryEnvelope geometries

[todddoerr]

I'm using http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/Geometry/GeometryServer/project and trying to project coordinates in an esriGeometryEnvelope.  I keep getting "The specified geometry is not in the correct format" message.

Here are my inputs:
Input Spatial Reference:    4326
Output Spatial Reference: 102039
Geometries:                    geometries={"geometryType":"esriGeometryEnvelope","geometries":[{"xmin":-127.987753,"ymin":40.611482,"xmax":-118.097294,"ymax":49.478615}]}

Format: HTML

Would somebody help me with the correct format, please?
Thank you.

[nicogis · Accepted solution]

I have tried and it runs:
http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/Geometry/GeometryServer/project?inSR=4326...

In geometries you have put 'geometries='