Cannot use expression variables in pipeline

[xzycn]

I have set an expression variable for image tag as document described, but an error "unable to parse variable name" when I run the pipeline.
The pipeline yaml:

[xzycn]

Update: the tags field should be a string not a array/list or map.
Like this:

tags: ${{ build.branch }}

the plugin step from web-ui has a wrong format.

[jimsheldon]

Thanks for reporting this @xzycn. Lists are currently broken in plugin settings, this is a known issue that should be fixed in the next release.