I am going to trying and summarize this as well as I can.
My standard object "Contact" has an external Id field called "Client ID". This is the unique identifier for a contact/customer.
I also have a custom object called "Products". I have tried to create a master look-up field that would link "Products" to "Contact". The field in "Products" is called "Client_Id__c, when I try to upload the CSV through the Bulk API V2.0
When I try to use the Bulk API v2.0 to upload this product information, I get the below error
"MALFORMED_ID:Client ID: id value of incorrect type: 98305:Client_ID__c --"
From my research this is suggesting that the malformed ID is because I need to use the salesforce ID and not the external id that I have listed on the "Contact"?