Begin Overlap and End Overlap return the actors once when event happens. The actors are not saved in the nodes, so when you call the Take Damage Event by Tick, there’s no reference to the actor, hence the error.
You can save the actor to a variable and work with it:
Or:
And keep in mind that Event Tick in fps-dependent; if you leave the tick interval at the default 0, the damage results will be different with different fps. You can use a timer instead.
