What makes a personalized birthday song work
A birthday song succeeds or fails in the chorus. If the name is sung clearly at least three times, the person hears it, laughs, and the video gets replayed. If the name only shows up once in a verse, it sounds like a generic track with a word swapped in. So the single most important line in your prompt is the instruction to sing the name in the chorus.
The second thing that separates a memorable song from a filler one is specificity. Two or three concrete details beat a list of adjectives: the marathon they finished, the cat that hates everyone but them, the fact that they still use a 2014 phone. Details give the AI something to rhyme with and give the listener a reason to grin.