From the article linked above: "GrapheneOS users are strongly encouraged to share this documentation with app developers enforcing only being able to use the stock OS. Send an email to the developers and leave a review of the app with a link to this information. Share it with other users and create pressure to support GrapheneOS rather than locking users into the stock OS without a valid security reason. GrapheneOS not only upholds the app security model but substantially reinforces it, so it cannot be justified with reasoning based on security, anti-fraud, etc."

You've probably blocked one of the external API points.