iCloud Calendar adding unknown invitations

[gnasher729]

Just had this on my iPhone 7 from who knows?? is this spam, I declined obviously, but worrying. It also came on my iMac, so obviously something on iCloud or a calendar that is synced?

Doesn't matter if you accept it. It's like a message at work: I might invite you to a meeting. You accept or decline, all it does is telling me that you accepted or declined. I can't force you to come to the meeting. They can't force you to buy their dodgy sunglasses.