Is the sweet syrup that drips from this plant poisonous please?

Welcome GOY. I think it best to assume it is possibly poisonous as the family to which it belongs has some poisonous members.
Asclepiadiasceae. is the family , but that spelling may not be quite right.

How do you know it's sweet?

I had a friend with this as a houseplant - she regularly used to lift off a drop and put it on her tongue - she's still alive and well!

My parents had Hoya at home, me and my brother used to lick this syrup daily all our childhood. I'm 30 now he is 27 all well and fine😉