Instructions for using and understanding content shouldn't rely solely on sensory aspects such as size, shape orientation, or sound. These are helpful and effective, but the information should also be conveyed in other ways.
1.3.3 Sensory Characteristics: Instructions provided for understanding and operating content do not rely solely on sensory characteristics of components such as shape, size, visual location, orientation, or sound.
How to fix:
Don't just rely on instructions like "Click the big round button in the middle of the page to log in". There should also be a text based label for the link as well.