A certification always consists of a theoretical and a practical part. For both parts, you need to score at least a 5.5 for both separately. In addition, the weighting is 50:50. So if you get a 7 for your theory and a 9 for your practical assignment, your final grade will be an 8. If in the opinion of the examiner (always an experienced senior trainer/consultant) you meet the requirements, then you have passed without further ado (except for the Master Black Belt, here there are always 2 examiners present).
If you do not meet it or if the examiner has doubts about parts, it is up to the examination board to assess and make a decision. If this leads to a "fail" verdict, you are entitled to a retake. In addition, the examiner will also indicate what is needed to still meet the requirements. So again, you have not necessarily failed without, for example, an "end-to-end" value stream analysis, but you do have considerably more to explain!
Fortunately, we see that the vast majority of candidates pass in one sitting. Only a small minority need a retake. This should inspire confidence: if you take Lean seriously, chances are you will succeed!