Its a very common issue and reproduce if you delete the podfile manually and create it again using pod init.

Use the following Steps to easily resolve this Issue but make sure to backup the native code if exist or backup the settings you make in the runner:

• Delete IOS folder.
• flutter create . (This will create the ios folder again and will sync the podfile with your flutter app).
• navigate to ios folder using "cd ios".
• pod install.

This will help you for sure. Best of luck