This just happened for the first time ever in my game tonight and it really surprised me. :open_mouth: My mouth literally fell open. :lol: Both relationship bars were maxed out, they were considered "soulmates", their needs were perfect, and the female sim had the whim to get married, while the male had the whim to propose to her. Once she rejected him, I paused the game and started looking around here to see if anyone knew what could trigger a rejection. I can't remember which thread it was on, but someone mentioned that entering into a relationship then following it too quickly with a proposal could be a problem. My female sim had a moodlet that said the timing wasn't right, so it seems plausible. All other sims I've played had been in relationships weeks upon weeks before proposing, whereas these sims had only been together a couple days. I also realized I skipped over the other things I've done in the past that resulted in accepted proposals, so I waited a few more sim days, applied the steps I normally follow, tried again, and it worked. Here's what I did in case it helps anyone... :smile:
1.) Wait at least a sim-week before popping the question.
2.) Make sure both sims know each other's traits and careers, and make sure their relationship bars are well-established.
3.) If you can, ensure both sims are in good moods and that their needs are met. Also, if possible, make sure they're without negative moodlets.
4.) Get the sims to flirt with one another until in "Flirty" moods and progress the conversation until it reaches a "Steamy" state. Perform only romantic interactions leading up to proposing, as performing friendly socials will cause the "Steamy" state to dwindle away.