Getting Your MAC Address - Arnold User Guide

Open the Arnold License Manager (in the Arnold menu for your Arnold plugin, click Licensing > Arnold License Manager)

In the Arnold License Manager, click File > Diagnostics

Scroll down and find the rlmutil rlmhostid information, which looks like this:

 rlmutil rlmhostid -q ether (1.38 sec)
==============================
1833da020992 020335733b80 00ee56c00001 005ff6cdd008  

Use the first MAC address in the list.