1. For technical reasons, auto update works only for the most recent theme generation. Old theme generations (2 years old) can be easily updated this way.
2. Please make sure you do not confuse secret API key with an Item Purchase Code.
3. Auto update is not available when using a child theme. Please switch to the parent theme, update it and activate the child theme back again. Then go to Theme Options -> Buttons -> and click SAVE.
4. Make sure you have not changed theme name.