Reference line for nominal values

[alon-aviv-ni]

Hi all,
I would like to add two traces - one of type 'box' and the other of type 'line'.
Line width is controlled whenever I plot numerical values - simply using the min/ max values to select my lint starting/ ending point.
However, I'm trying to get my line start/ end according to the nominal value I have (e.g., 'T1') so I cannot use x0 and x1 as numerical values.
When trying to set: x0: 'T1' and x1: 'T1' I get a dot and not a line.
Is there a way to set the start/ end point according to the box plot width?
Following an image of what I'd like to achieve - a box plot with two reference lines/ limit lines: