I made a template with a command in the repo: https://github.com/safe-global/safe-apps-sdk/tree/master/packages/cra-template-safe-app

After yarn start, I added localhost:3000 at 'Add custom app' in the gnosis UI, and got the error: The app doesn't support Safe App functionality

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1 Answer 1


You can see the issue by opening your browser console.

Most likely the issue is due to CORS error.

You have to make sure that the link you provide is using https and that the server's response provides the following header:

Access-Control-Allow-Origin "https://app.safe.global";


Access-Control-Allow-Origin "*";

as stated in this answer: https://ethereum.stackexchange.com/a/149561/76188

Personally I don't recommend using "*" as it would introduce vulnerabilities for your users.

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