St Johnstone thought the whistle had been blown before the ball crossed the line but are now satisfied this was not the case and are not pursuing the matter further.
The SFA advised on Saturday evening that they had reviewed the audio and were satisfied MacDermid waited until the ball had crossed the line before blowing his whistle.
This then allowed VAR to check whether the award of a foul against Dessers was correct.
The last-16 tie ended 2-0, with Ross McCausland adding a second goal in added time.
Immediately after the defeat, St Johnstone manager Craig Levein said: “Everybody stopped because of one or two things. Either they’ve stopped because they heard the whistle or they’ve seen the referee giving us a free-kick.
“I think the referee’s made a mistake. And I’d love him to come out afterwards and just say, ‘look, I’ve got that one wrong’.”