Task: Uploading a file to a Slack channel

n8n workflow JSON:
{"nodes":[{"name":"On clicking 'execute'","type":"n8n-nodes-base.manualTrigger","position":[160,300],"parameters":{},"typeVersion":1},{"name":"Download the file","type":"n8n-nodes-base.httpRequest","position":[420,300],"parameters":{"url":"https://n8n.io/_nuxt/img/sync-data-between-apps.a4be8c7.png","options":{},"responseFormat":"file"},"typeVersion":1},{"name":"Post to Slack","type":"n8n-nodes-base.slack","position":[640,300],"parameters":{"options":{"channelIds":["C02GP22NHJ6"],"initialComment":"This is the file"},"resource":"file","binaryData":true,"authentication":"oAuth2"},"credentials":{"slackOAuth2Api":{"id":"124","name":"cloud_demo"}},"typeVersion":1}],"connections":{"Download the file":{"main":[[{"node":"Post to Slack","type":"main","index":0}]]},"On clicking 'execute'":{"main":[[{"node":"Download the file","type":"main","index":0}]]}}}