The Watershed tool, located at https://developers.arcgis.com/rest/elevation/api-reference/watershed.htm, fails with the error, "ERROR 000735: Input Features: Value is required", even when all parameters are valid.
Cannot reproduce this error. Please make sure your point is within the processing extent as shown in the is map: https://developers.arcgis.com/rest/elevation/api-reference/source-data-for-hydrology-analysis-tasks.htm