1x: Since symfony/serializer 6.3: "JoliCode\Slack\Api\Normalizer\JaneObjectNormalizer" should implement "DenormalizerInterface::getSupportedTypes(?string $format): array".
And this:
Warning: Your XML configuration validates against a deprecated schema.
Suggestion: Migrate your XML configuration using "--migrate-configuration"!
Should resolves this:
And this:
No other modification.