It is best not to assume that you can write the function better than AI. If the AI believed that what looks like JSON is what is to be sent to dall-e, it might omit required parameters.
Your alien works today, with what I know is required to get quality on top of custom instructions:
dalle tall image: {
“prompt”: “A full-body portrait of a humanoid alien. The alien has an elongated head, large, expressive eyes in a color not typical for humans, and skin in unusual shades like green or blue. The alien’s limbs are longer and more slender than a human’s limbs. The background is abstract and ethereal to enhance the alien atmosphere. Alien’s clothing is futuristic or non-traditional, emphasizing the creature’s uniqueness. The alien figure stands in a natural pose, allowing a clear view of its characteristics and features. Sharp, detailed, textured imagery. Full-body-length image in tall aspect ratio.”
}
(used without rewriting)