You are mixing two concepts: chapter numbering and list numbering.
The Heading n family of paragraph styles marks the paragraphs as belonging to the document outline. There is one Heading n per level. Chapter numbering is controlled by Tools
>Chapter Numbering
and you must absolutely never try to change it/customise it with the toolbar button which are intended for lists.
Your “Heading text text text” is styled with Heading 3, without any addition. By default chapter numbering in not enabled. refrain from adding numbers with the toolbar button, you’ll be heading into trouble. Instead, use Tools
>Chapter Numbering
to describe level per level how your numbering should look like.
Your “text text text” paragraph are the at level 4 and should be styled Heading 4. Once again go to Tools
>Numbering
to suppress display of numbers for levels 1-3 leaving only the alphabetic numbering of level 4.
Don’t use Format
>Bullets & Numbering
otherwise numbering will not be synchronised with your Heading n paragraphs.
I won’t give you detailed step-by-step procedure so that you take the time to experiment and discover the feature. It is the best way to learn. In particular, learn and make profit of the difference between outline (chapter) paragraphs and lists.
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