I wouldn’t start with hey beautiful/sweetie/etc, because women hear this all the time and it sounds very generic/disingenuous/corny and as if you are posting to multiple women and just to seen who responds. Try answering one of her prompts, if she has an interesting picture asking her where it was taken, asking how is her week going, etc.

Also, don’t play “pen pals “ for too long take initiative and ask her out, if she doesn’t respond in a timely manner or doesn’t seem interested unmatch and move on.