Hello,
I recently had some trouble creating buffers, and after some troubleshooting on the js api forum it turned out that I was using an outdated Geometry Service. I was using tasks.arcgisonline.com but it seems like that server is an old version so instead I was told to use sampleserver6.arcgisonline.com.
We have an ArcGIS Online Organizational License, which we use to host feature services. We prefer to develop our own apps in house rather than use the arcgis online map viewer. My question is, which server should we be requesting from when completing geometry services?