What is the duration of this spell? As phrased, it isn't instantaneous, it's some sort of ongoing curse ("Whenever the target becomes affected by a spell with a duration"). And there's a mention in the "Success" line that limits the duration of the effect to 1 minute. But the Failure line doesn't indicate how long it lasts if the target fails their initial save, nor any method for the target to end the curse.
What is the duration of this spell? As phrased, it isn't instantaneous, it's some sort of ongoing curse ("Whenever the target becomes affected by a spell with a duration"). And there's a mention in the "Success" line that limits the duration of the effect to 1 minute. But the Failure line doesn't indicate how long it lasts if the target fails their initial save, nor any method for the target to end the curse.
I think the spell has instantaneous duration (otherwise it would trigger the curse itself) but the curse lasts until removed by a general curse-removing method (like remove curse). This could certainly stand to be clearer.