If you cannot see the code as you are typing it, you are mostly likely using an uncertified Android Box which by default is using the touch screen UI. This is very easy to fix.
Please switch to TV UI. To do that -
You will see this error due to 2 reasons
You have mistyped your code - In which case, please check each character (specially 0s and Os) and try again.
You are using the touch screen UI on your TV due to which you cannot see the code as you are typing. Please see the solution above 'Cannot see when typing'.
Your code has been disabled - If you have claimed a refund against your code, it will be disabled. Please reach out to your reseller if you need more information regarding this.