Create a record in an object with lookup fields through java soap

I am pretty new with Salesforce and I am doing an integration where I have to update Salesforce with data from a Business System.
I have a problem when trying to create new records in an object with lookup fields from another parent object.
I am using java soap protocol with a partner connection and the field I am trying to update is of Master-Detail type.
I can update it successfully if I enter the Salesforce ID for the value, but not when I enter the actual value that should go in the field.

Quickbooks Web Connector “Response is not well-formed XML” error

We are using the Quickbooks Web Connector (QBWC) with the Consolibyte Quickbooks PHP Dev Kit. We have had a QBWC job working with this software for 4 years without major issues; however, now we are adding an additional QBWC job to access a different QB company file and a different handler. Every time this job runs it gets an error “Response is not well-formed XML”: