The pair, who both have name suppression, met on dating app Grindr and later had sex.
On Wednesday afternoon, Judge Jim Large told the jury at Christchurch District Court a legal issue has arisen and a mistrial declared as a result.
The reasons for the mistrial have been suppressed.
The trial began on Tuesday, with Crown lawyer Sean Mallett saying prior to the pair having sex, the defendant had mentioned being rewarded for the encounter, but they had not agreed on an amount or method of payment.
The pair exchanged messages after the encounter about the amount of money.
However, when no payment had been made by the next day, the defendant went to the complainant's house and put up a cardboard sign demanding payment, and saying a lack of payment would equate to sexual assault, Mallett said.
Later that day, the complainant paid the other man $250.
After that, the pair continued to exchange messages, which the complainant said equated to blackmail.
In one of the messages, the accused said he was feeling discontented with their encounter and felt like he had two options: either going public, or going on an overseas trip to take his mind off his troubles. However, he could not afford a holiday, he wrote.
The defendant's lawyer, Nikki Hansen, said the question for the jury was whether her client was attempting blackmail, or simply letting the complainant know he was unhappy and wanted an apology.
She questioned whether the accused had consented to all of the sex acts. In some of the mGrindr blackmail trial aborted essages from the accused, there were references to sexual assault.
Hansen said an accusation of blackmail would be an excellent defence to a charge of sexual assault.
