Are you sure those Webflow CMS Item IDs are valid? How did you get them into Airtable?
What’s the validation error message that the Webflow API is returning? There should be a err attribute in the JSON response.
It might be simpler to use PowerImporter to automatically sync your Airtable to Webflow whenever a new form is submitted. It takes care of all the single and multi-reference fields for you, and you don’t need to manage any of the CMS Item IDs either.