Let's check this out...

.woodpecker/build.yaml

@@ -37,6 +37,11 @@ steps:
     commands:
       - set -e
       - echo "=== Pushing to registry ==="
+      - |
+        if [ -z "$REGISTRY_USERNAME" ] || [ -z "$REGISTRY_PASSWORD" ]; then
+          echo "ERROR: REGISTRY_USERNAME or REGISTRY_PASSWORD is empty - check secret names match Woodpecker (gitea_registry_username, gitea_package_token)"
+          exit 1
+        fi
       - echo "$REGISTRY_PASSWORD" | docker login "$REGISTRY_URL" -u "$REGISTRY_USERNAME" --password-stdin
       - docker push $REGISTRY_REPO:${CI_COMMIT_SHA}
       - docker push $REGISTRY_REPO:latest