The ID value that Airtable is giving back to you—beginning with “rec”—is Airtable’s internal ID for the record. Airtable always creates its own ID for every record, even if the user chooses one themselves for the record’s primary field. That ID isn’t being stored in the literal “id” field that you created; Airtable is just returning it to you in case you need to use it in later steps that require an Airtable record ID.
The ID that you’re passing in is still being stored in a field named “id”, which will not clash with Airtable’s internal ID. However, you can’t use them interchangeably. If a later step in the scenario requires an Airtable record ID, you can’t pass your own ID. It needs to be an Airtable record ID.
Does that make sense?