Hello @Claudio Acosta The REST API Key must remain secret — that’s why OneSignal warns you not to expose it publicly. But that does NOT mean you shouldn’t enter it anywhere.

The key you created should be placed in: Studio → OneSignal → REST API Key ----- It's exactly the one you created according to the screenshot you sent.

Previously, OneSignal only registered your email subscription because the REST API Key wasn’t configured as dear @LeonidS mentioned.

But do NOT share your REST API Key anywhere publicly!!!