What is the issue?
PDF/UA > Logical Structure > Structure Elements > Headings > First heading level > First heading is not on the first level
What does it mean?
In every document, the first heading has to be an H1. The first heading in your PDF, however, is not an H1.
How to fix it?
Change in the task pane "Logical Structure Tree" the first occurring heading-tag to "H1". Be careful that there is no jump in the heading levels. You must not miss a level: an H1 must not follow an H3, for instance