Composite Graph API: Associate reference with an ID from a GET

Question

I'm trying to use the composite graph API to associate a record to a parent using just a GET for the parent to get the ID.

My request looks like this

{
    "graphs": [
        {
            "graphId": "graph1",
            "compositeRequest": [
                {
                    "method": "PATCH",
                    "referenceId": "opportunity",
                    "url": "/services/data/v55.0/sobjects/Opportunity/External_Id__c/8f0086e5-a1e0-40da-bbde-4cff20d61e8e",
                    "body": {
                        "Loan_Processor__c": "John Smith",
                        "Processing_Date__c": "2023-03-10",
                        "Processing_DateTime__c": "2023-03-10T20:09:00Z",
                        "Lock_Rate_Requested__c": true,
                        "Lock_Request_Base_Rate__c": 99.99,
                        "Lock_Request_Count__c": 4,
                        "Sell_Side_Investor_Phone__c": "925-467-9999"
                    }
                },
                {
                    "method": "GET",
                    "referenceId": "loanApplication1",
                    "url": "/services/data/v55.0/sobjects/Loan_Application__c/Application_Id__c/8f0086e5-a1e0-40da-bbde-4cff20d61e8e___borrower1"
                },
                {
                    "method": "PATCH",
                    "referenceId": "loanApplication1Employment1",
                    "url": "/services/data/v55.0/sobjects/Employment__c/Employment_External_ID__c/8f0086e5-a1e0-40da-bbde-4cff20d61e8e___568438598",
                    "body": {
                        "Loan_Application__c": "@{loanApplication1.id}",
                        "Employer_Name__c": "Salesforce"
                    }
                }
            ]
        }
    ]
}

This gives me back an error:

Invalid reference specified. No value for loanApplication1.id found in loanApplication1. Provided referenceId ('loanApplication1.id') must start with a letter or a number, and it can contain only letters, numbers and underscores ('_').

However, if I change the 2nd composite request from a GET to a PATCH it works as long as I set a body.

So this request works:

{
    "graphs": [
        {
            "graphId": "graph1",
            "compositeRequest": [
                {
                    "method": "PATCH",
                    "referenceId": "opportunity",
                    "url": "/services/data/v55.0/sobjects/Opportunity/External_Id__c/8f0086e5-a1e0-40da-bbde-4cff20d61e8e",
                    "body": {
                        "Loan_Processor__c": "John Smith",
                        "Processing_Date__c": "2023-03-10",
                        "Processing_DateTime__c": "2023-03-10T20:09:00Z",
                        "Lock_Rate_Requested__c": true,
                        "Lock_Request_Base_Rate__c": 99.99,
                        "Lock_Request_Count__c": 4,
                        "Sell_Side_Investor_Phone__c": "925-467-9999"
                    }
                },
                {
                    "method": "PATCH",
                    "referenceId": "loanApplication1",
                    "url": "/services/data/v55.0/sobjects/Loan_Application__c/Application_Id__c/8f0086e5-a1e0-40da-bbde-4cff20d61e8e___borrower1",
                    "body": {
                        "Borrower_First_Name__c": "Bob"
                    }
                },
                {
                    "method": "PATCH",
                    "referenceId": "loanApplication1Employment1",
                    "url": "/services/data/v55.0/sobjects/Employment__c/Employment_External_ID__c/8f0086e5-a1e0-40da-bbde-4cff20d61e8e___568438598",
                    "body": {
                        "Loan_Application__c": "@{loanApplication1.id}",
                        "Employer_Name__c": "Salesforce"
                    }
                }
            ]
        }
    ]
}

The only thing I changed was the GET to a PATCH and added a body only because it's required.

I don't want to do a PATCH for the 2nd request (the Loan_Application__c object) because I don't need to update it. I just want to do a GET so I can use the id in the 3rd request to associate the Employment__c to it's parent Loan_Application__c.

What am I missing?

UPDATE: I discovered that the property for the id is case sensitive. If the 2nd request is a GET the reference in the 3rd request has to be @{loanApplication1.Id} but if the 2nd request is a PATCH the reference in the 3rd request has to be @{loanApplication1.id}. Notice the difference of the capital I in Id vs the lower case i in id.

I'm not sure why this happens or if there is any way to resolve it.