How can I delete the notification in my calendar

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Calendar -  Remove spam from on your iPhone

Calendar Spam

Calendar and Photos SPAM Invites

Calendar and Photos SPAM Invites (2)

Hi! This probably happened when an unsecure website asked you “Open this page in calendar?”, and you clicked open. Like that it adds an account with spam offers. To remove it go to Settings>Calendar>Accounts, and if you see an unknown account like the one in this photo, select it and click remove.

Take care.