I’ve never experienced a flashing green light. Here are some questions that may help you isolate the issue:
1. What level is your battery at? Is it completely dead or just partially dead?
2. Is the wall outlet good? Can you use another outlet to see if that fixes the issue?
3. Is the charging plug connected correctly to the bike?
4. Is the bike powered on or off when you charge?
5. Have you called your local bike store? They may have another charger you can use to test if it is your charger or your battery/bike.