Is it possible to create a group directly under the Probe via the API?

The target ID would be the ID number of the probe itself. When you click on a probe, at the upper right hand corner there will be the ID# like below.

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Is it possible to get the ID of the probe through the API by searching it's name?

All of the calls through the API require that you use the ID of the sensor / group / device since they can be named similarly in PRTG.

Using /api/table.htm?filter_name=[name of thing], it's possible to get the ID of group/device/sensor through the API. I don't see an option to get a list of probes through in the API docs, so I was wondering if there's another way get the ID of a probe via the API.

The call would actually be /api/table.xml?filter_name=probe device which would give you a list of the probe devices but the ID's are not included in there.

<?xml version="1.0" encoding="UTF-8"?>
  <>
   <prtg-version>13.3.6.2768</prtg-version>
   <item>
    <group>RemoteProbe2</group>
    <device>Probe Device</device>
    <sensor/>
    <status>Up </status>
    <status_raw>3</status_raw>
   </item>
   <item>
    <group>RemoteProbe</group>
    <device>Probe Device</device>
    <sensor/>
    <status>Up </status>
    <status_raw>3</status_raw>
   </item>
   <item>
    <group>Local probe</group>
    <device>Probe Device</device>
    <sensor/>
    <status>Up </status>
    <status_raw>3</status_raw>
   </item>
  </>