All your tests do not pass in the notebook. There is no function called update_parameters, but that is required. There are clear error messages saying that in the notebook when you run it.
Here’s what the “Exercise 6” section looks like in your notebook:
Here’s what that looks like in a clean notebook:
So how did that happen? It looks like you must have deleted the update_parameters cell and replaced it with a copy of the backward_propagation cell. That would have taken some explicit actions to do.
My suggestion would be to start over again by getting a clean notebook. Here are the instructions for how to do that. You can save and reuse your previous functions by copy/pasting them over, but you need to be careful not to change the fundamental structure of the notebook when you do the copying.