Training Stream - Spline Importing w/ - Jan 10th - Live from Epic HQ

Hey, Have been following the tutorial, but it has some trouble with curves…said in the video that there was some math error, and swipped to another project to show how it propertly works, but did not explain what was wrong and now I am experiencing that issue…
Can Anyoone please explain what was wrong in the maths? thought was the final part of the tangents but not sure the exact point