Does PBA-E support sales sub-categories? For example customer goes to
Control Panel > Buy more services selects sales category "Web hosting", on next screen selects sub-category "Linux Web hosting' or "Windows Web hosting", then selects plan, etc.
Support for sales sub-categories is not implemented in PBA-E. There is feature request #PBA-56256 to implement this functionality.
For now the only way is to do grouping on sales category level (i.e. in exmaple above instead of creating sales category "Web hosting" create 2 different sales categories - "Linux Web hosting" and "Windows Web hosting")