Trouble showing a designated month where an event happened on a line graph

[datadelta]

I have a line graph that charts activty by customer for 2 years.  What I'm trying to show is a specific date that a designated event occured.  I know I have done this before but I cannot remember how to do it now.

here is an image of the graph and the designated date field.  what I know can be done (somehow) is to have the January 2022 date show up on the graph as a designated point in the graph.  I believe I had previously had a vertical line being shown to reflect whatever that first date of sale was.

Any help would be appreciated.  Thanks.

[lbendlin · Accepted solution]

maybe you did that in Deneb?  It has a couple nice examples for using rules etc as highlighters.