Which one is the frame number?

I would suggest that when you register your bike, put both numbers/strings into the system.

If you only put one, then some day when its been recovered after a theft, the operator might put the other number in, and not score a match.

Whichever is the correct serial number doesn't really matter in this specific case.

If some other bike duplicates one block of text, then the description (colour/size/etc) and the other number will help differentiate them.

Good work with pre-registering your bike before there's any incident. Its too late once the bike's been pinched.

You will need to contact Leader Fox to answer this question. The Leader Fox website does not have any information on which of those numbers is the bicycle serial number.

Here is a link to the manuals for their bikes.
Their manuals do contain information on the serial number for the motors on their e-bike which is not the same thing as the serial number for the whole bike. Here is a link to their contact page