How to pass multiple values using IN operator in salesforce SOQL

Hi team ,

In SFDC integration , we are using SOQL query in operation to fetch some data for a given financial id , need to understand how to write the query to fetch data for multiple values involved.

Current implementation - concat(Select shareclass_c from breakdown_c where financial_id= ' ''' ,ri !finId) ;

How to write above for fetching data for multiple financial id's involved , ri! finId will be of multiple type of string . Tried to replace above = with IN operator in where clause, it shows malformed SQL as integration error.

Thanks