What's the difference between the application number and patent number of the invention patent?

The application number is the number given after the patent application is filed and accepted. This is because the patent application has not been formally examined, and it is uncertain whether it can be authorized in the future;

The patent number is the number given when the patent right is granted after examination and approval.

Just like the difference between the admission ticket number you gave when you took the exam and the certificate number after you took the exam.