How to pass multiple values using IN operator in salesforce SOQL Query

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 Id, Name, Reference_Type__c, System__c, Seq__c from SRS_Service_Request_Related_Order__c where RO_Service_Request__c " ,"='",ri!serviceRequestNo,"'");

How to write above for fetching data for multiple financial id's involved , ri!serviceRequestNo 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