Please follow the following Procedures
Step 1: Go to the following website
Step 2 : enter your mobile number ,then hit the submit button, you will receive OTP, then click verify OTP.
Step 3: Once the OTP is entered, you will receive a SMS from GST portal, to download the verification app.
Click the link in you mobile and install the app.
Step 4: This is from untrusted source. You need to enable the settings to trust this.
Step 5: Once you have installed the app. Just scan the QR code. it will show GST number, Recipient GST number, the invoice details, IRN number, etc.