There isn't really much to go on, but I will mention a few possibilities
the tube and end caps are not well threaded, it would ooze out where the cap meets the tube
Your head isn't screwed all the way down, leaving a gap between head and post. It would leak down the post and through connector
The silicone cap that sits on the head isn't making a clean connection with the top-cap. Pop the drip tip out and look down the hole. Is the connection with silicone neat or is it crooked. It would leak out the tip or down the connector tube.
Any wick threads/bits screwed into the head/post connection by accident. The
juice can follow them and wick right through the post.
Those are my tips. Also, as someone else asked, are they Vision brand? I have had clones/knock-offs. They sucked (and leaked, lol)