My archive-posttype.php template is not loading

as determined in the comments, the page URI is ?post_type=photos&genre=boudoir

The reason why "archive-{$post_type}.php" isn’t used in this case is because the page is a taxonomy archive and not a custom post type archive. WordPress is looking for taxonomy-genre.php instead of archive-photos.php, and not finding it, is defaulting back to good old archive.php. Here’s a wonderful cheat-sheet on the template hierarchy, which is so useful it’s probably worth tattooing on your forearm.

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