Assuming you've already made sure the Slack account connected to Airtable has access to the desired channel, you can manually force the channel selection by grabbing the Slack Channel ID and feeding that to Airtable automation as a "dynamic" field in...

For anyone else getting this error, check if your "Create a record" automation is trying to link a record using a Display "Name" instead of "ID". For me, the error came up after the automation had been running for a while without issue, so it was har...