For older iOS devices (iPhone 4s, iPad 2 running iOS 6-8), a jailbreak tweak called "LocalIAPStore" can simulate unlock code responses. This bypasses the server entirely.
Character Specialties: Remember that different characters have unique abilities. If you can't progress, switching your character might be the "code" you actually need. Some characters make it easier to clear specific patterns, effectively unlocking the next stage through gameplay efficiency. Bubble Bash 2 Unlock Code