I purchased a quality 3/5 Maw of the Deep in the marketplace. When I try to use it to upgrade my quality 5/5 Maw of the Deep from rank 3 to rank 4 at the Apprentice Jeweler the gem appears in the UI but cannot be selected in the upgrade menu.
You’re reporting this issue in a forum dedicated to bugs in the Bnet app on phones. Please visit the game title forum.