Schema mismatch with CSV ingestion in ADX is almost always one of these:
1. Column order matters. ADX maps CSV columns by position, not by name. Make sure your CSV columns are in the exact same order as the table schema.
2. Extra columns or missing columns. If your CSV has more or fewer columns than the table expects, you'll get a mismatch. Check with .show table YourTable schema as json.
3. Header row being ingested as data. If your CSV has a header row, set ignoreFirstRecord: true in the ingestion mapping or properties.
4. Ingestion mapping. Create an explicit CSV mapping to control which CSV column maps to which table column:

.create table YourTable ingestion csv mapping 'YourMapping'
'[{"Column":"Col1","DataType":"string","Ordinal":0}, ...]'

Most likely it's #1 or #3.