Now.....
Is that the 8th digit (right-hand end)?
OR
The 1st digit (left-hand end)?
I would presume a 'leading' zero? - But one never knows!
It's 8th digit right hand end. For example,
www.playmodb.org shows an excerpt from an original instruction sheet showing a 7 digit part number, but also shows the 8 digits to be used.
The older instructions had 7 digit part numbers:
But the newer instructions with the same part add the zero to the end:
It's also notable that the playmobil parts department wants the empty spaces in the part number removed. If you try to use the spaces in the USA, they may ask you to remove the spaces if there is a large order with many part numbers, but if it's a small order they might change it themselves. If you leave the spaces in on the web store of other countries you get something like this telling you to remove the spaces and use 8 digits:

But if you remove the spaces and use the 8th digit 0 you get this:

Notice their inconsistency in referring to it as both a part number (when asking for it without spaces) and product number (near the price). They also have an inconsistency in sometimes referring to set numbers as product numbers. So If we are to charitably assume their competence, 'product number' would seem to be a generic blanket term applying to both part numbers and set numbers.