How to check the patent number? Why can't I find this patent number?

No related patents were retrieved! The reason why the relevant patents were not retrieved may be: 1. The invention-creation is in the state of undisclosed (referring to the invention patent application), undisclosed (referring to the utility model or appearance patent application) and confidential patent application. 2. The entered search criteria are too strict. Please use broader search criteria and search again. 3. The search criteria were entered incorrectly.