There are many reasons why a QR code is not working correctly. At first check your entered data. Sometimes there are little typos in your URL that break your QR code. Some QR codes (like vCard) contain a lot of data. Try reducing the data you entered for your QR code when possible. This can make it easier for QR code scanner apps to read your code. Try to remove the logo in your QR code and check if this helps. Also make sure that there is enough contrast between the background and foreground of the QR code. The foreground should always be darker than the background. Here is an article about