Troubleshooting

This page lists the most common symptoms when running the SDK Demo App and how to resolve each one.

Symptom	Resolution
`Unsupported class file major version` on sync	The Gradle JDK is not 21. See Step 2 of the Quick Start.
`Could not find com.pagonxt.sdk:brazil-hml`	The bundled local Maven repository for the variant is missing. Confirm that `apolo-sdk-local-maven/brazil/<buildType>` exists — for example `brazil/hml` for the `brazilHml` variant.
The QR Code still carries the sample credentials	The Compose preview was not rebuilt after you edited the payload. Open `MandatoryCredentialsQrCode_Preview` or `FullCredentialsQrCode_Preview` and click Build & Refresh. See Step 4 of the Quick Start.
Credentials saved, but the warm-up fails and the main menu does not appear	The warm-up status code names the cause: `401` for an invalid `clientId` or `clientSecret`, `404` for a terminal that is not registered, `400` or `422` for the `terminalCode` or sub-merchant values. See the warm-up errors in the Error Codes Reference.
The Setup screen does not appear and the app keeps the previous credentials	They persist in the app database after the first save. Clear them with the reset button in the Home screen header, through Settings → Apps → Apolo DevKit → Storage → Clear data, or by reinstalling the app.
App opens, but sale, refund, or printing fail	The terminal is not ready. Check the POS itself and the Platform and Middleware services in Prerequisites.
Colors or receipts do not change	They are build-time customizations. Trigger a `reinitialize(…)` — a `shutdown()` and `setup(…)` cycle — to apply them.

Next steps

Quick Start — the build and run steps referenced above.
Error Codes Reference — the SDK’s result codes and cause categories.