How to initiate sex with a fwb?

So obviously most would send the “you up” text to a typical fwb, but my fwb is actually a true friend, like we hang out all the time. So sometimes the mood strikes and we wanna go for it, but it feels weird to just jump on top of them, or just be like “wanna fuck?” in the middle of talking about our day.

I feel like this is (surprisingly) a unique situation wherein we don’t just text and meet up for sex, but also not romantic or flirty where I can ease it in after a passionate kiss or while cuddling. In fact, it feels pretty strange because the rest of our interactions are platonic and friendly, so it feels weird to just jump into it without being flirty or anything really leading to it. We’ve talked about it and they didn’t really have any suggestions either.

How on earth do I initiate with my partner when we’re just normally hanging out as friends?