And after pleading guilty in Beenleigh Magistrates Court, Isaia has become the first person to be found guilty in a landmark case focused on online abuse.
The extent of the messages sent to the official, TMO Brian MacNeice, were not revealed, but were understood to mention his wife and children.
World Rugby chief executive Alan Gilpin welcomed the conviction, as the first of its kind towards abusers of match officials.
“The vile and toxic abuse is an all too common occurrence for many sports men and women and public figures,” he said.
“We hope that this sends a very strong message to online trolls that such behaviour is totally unacceptable and that the sport and the authorities are prepared to take action.”
Isaia was identified by Signify Group, a digital firm engaged by World Rugby to monitor social media for abuse.
In particular, Signify Group made use of an Artificial Intelligence programme called Threat Matrix to identify any alleged abuse.
Throughout the World Cup, 1.3 million posts were monitored, with 54,000 identified as potentially containing abuse.