I try to add ssh key to my project but 'Someone has already added that SSH key' warning always showing. And I don't know where that ssh key has been used.
Hi, @Wira Sakti, welcome to Atlassian Community!
As we will need to know the public ssh key to further investigate this case, I have created an internal ticket for you using the email of your community account, so you don't have to share this information here.
You should have received an email with a link to the support ticket. Just in case you haven't received it, please feel free to let me know and I can post the ticket URL here. The ticket will be visible only to you and Atlassian staff, no one else can view its contents even if they have the URL.
Please feel free to let me know if you have any questions.