I tried to reply to this post from 6 YEARS AGO... https://community.graphisoft.com/t5/Modeling/Can-someone-explain-Issues-vs-Transmittals/m-p/275239
but this is another example of archicad evolving over time and being very confusing for anyone who hasn't been using the tool for 10+ years... there is absolutely no reason we should still see "issue" AND "transmittal" in archicad change markers, layout book settings, etc... if they mean the same thing, they should say the same thing.
Every time I give a 'how to' lecture on revisions, I have to give an annoying history lesson on Archicad terminology.