This may be because you have entered the wrong phone number in the app. You can check this in the following way.
The page where you receive the SMS code contains a line that says
“send code by email instead”.
You will receive a link in the email. When you click on it, you’ll go straight to the app if you’ve accessed your email on your phone.
Once in the app, go under the three bars in the top left corner and select “account”.
There you can verify that you have entered the correct phone number. In case of wrong phone number change this and the SMS code will work in the future. The SMS code is a one-time code, so you’ll get a new one every time you need to log in again.