expport PDF as PDF/UA

I am exporting it as Interactive PDF with "Create Tagged PDF" selected.

In InDesign I did use the Menu "Edit All Export Tags" in Paragraph Styles Options to add a PDF tag (p or H1 to H6 or Artifact) to each Paragraph Style.

I know the export won't be perfect and I found how to correct most problems til now.

By @danp80169074

That's good. You also can set the tags for each style in its definition, under Export Tag. The lower section of that dialogue is for PDF (don't worry about the top part, it's for HTML & EPUB).

However my client did point out to me that some tags should be in another order. In my export I have <Art><Sect>Text<Sect><Art> and it should be in fact <Sect><Art>Text<Art><Sect>.

Have I done something wrong? Must I do some settings?

From what you describe, it looks like you're wondering about both the actual grouping tags used (<Art> and <Sect> in your example), how they are used, their nested structure, and their reading order/sequence.

Your original order is correct:

     Article <Art>

          Section <Sect>

             Text/Content here

(There are no visible closing tags in PDF — that's in XML and HTML — so ignore the closing <Sect> and <Art> in your example.)

Per the original definition and interpretation of PDF/UA-1, articles are larger chunks of grouped information, and sections are smaller chunks, such as sidebars and short copy related to a larger article. For a list of PDF/UA-1 tags and their suggested usage, see our blog at https://www.pubcom.com/blog/2020_05-02_tags/pdf-ua-tags.shtml

Although probably permissible, your client's suggested nesting sequence isn't correct or the best sequence.

Hope this helps.