Follow these steps to check what might be wrong and if this doesn't help, please contact us at contact@hwpotraining.com.
See below:
Empty spaces.
Verify you did not mix up 0 (the number) and O (the letter). This is a common mistake we have seen.
Make sure the code can be used on that specific program.
Make sure the code is still active.
If you have tried all of those possible solutions, please email contact@hwpotraining.com and provide:
The code you're trying to use
The specific HWPO program you're trying to use it on (this is so we can recreate the error you're seeing).