Hi - I'm pretty sure I have a multi-platform subscription; and it's active on my computer but not on my mobile. I can't find the account ID/key. Can you please help?
If it is not possible to find purchase/confirmation letter in your mail-folders (mail-service) -- maybe it is good to contact direct F-Secure Support Channels (chat as example) as most valid designed step:
With information about your purchase - most likely - Support with abilities to re-trigger mail-letter with credentials (licence activation key or so).