Dimension Linear command makes zero-length dimension

I want to make a vertical dimension of size 80mm using the command line.

Having selected the Linear Dimension, I inputted 0,0 as First Extension Line Origin
and 0,80 as Second Extension Line Origin.  And I get a line of 0 length.

https://docs.librecad.org/en/2.2.0_a/guides/annotate.html#dimensioning

Use Aligned or Vertical for your case instead.