Error converting data type VARCHAR to DECIMAL

I run an export from an Oracle table to csv file and have the csv on data lake. I scripted the Synapse destination table columns datatypes so they are correct. While loading with copy data from lake to Synapse I get:
PolybaseOperationFailed,'Type=Microsoft.DataTransfer.Common.Shared.HybridDeliveryException,Message=Error happened when loading data into SQL Data Warehouse. Operation: 'Polybase operation'.,Source=Microsoft.DataTransfer.ClientLibrary,''Type=System.Data.SqlClient.SqlException,Message=HdfsBridge::recordReaderFillBuffer - Unexpected error encountered filling record reader buffer: HadoopSqlException: Error converting data type VARCHAR to DECIMAL.,Source=.Net SqlClient Data Provider,SqlErrorNumber=107090,Class=16,ErrorCode=-2146232060,State=1,Errors=[{Class=16,Number=107090,State=1,Message=HdfsBridge::recordReaderFillBuffer - Unexpected error encountered filling record reader buffer: HadoopSqlException: Error converting data type VARCHAR to DECIMAL.,},],'"
1. There is no reference in the output log regarding the column that fails. How do I know which column fails?
2. As per (https://learn.microsoft.com/en-us/azure/data-factory/connector-azure-sql-data-warehouse?tabs=synapse-analytics#staged-copy-by-using-polybase), if I use staging it should fix if the source data is not natively compatible with Polybase. Is there any way to still use “Copy data”, or I should better chance to data flow (and add derived columns decimal for any datatype transformation