Fonts are not Type 1 PostScript (exceptions)
This check flags up when Adobe PostScript Type 1 fonts are used in the InDesign document.
PostScript Type 1 fonts, as their name suggests, were intended for print production using Adobe PostScript. They are an old font format which have largely been superseded by the later OpenType format as PostScript Type 1 fonts are not supported in digital and web publishing.
Adobe announced they were stopping supporting PostScript Type 1 fonts in any new software released after 2021.
Note that Type 1 fonts will no longer appear in InDesign's Font menus and must instead be replaced using InDesign Type menu > Find/Replace Font:
PostScript Type 1 fonts show their Type as ‘Type 1’ and warning signs alongside their name in Find/Replace Font’s dialog.
Fix this problem by finding and activating a different font format in InDesign or in some cases by substituting for other fonts.
There may be some cases, e.g. for minor amendments to backlist projects, where the user wishes to make an exception and continue to use GreenLight. If so, in GreenLight’s dialog click Allow use of these fonts for this document:
Adobe InDesign Font help
Apple FontBook help