Datacap webservice does not process the vscan task

We are running Datacap 9.1.1 on Windows 2012.
We have a Datacap application based on the standard template that we need to call via web service.
I tried to simulate the process using Postman (similar to Fiddler) to generate the REST calls. Our input files are in a folder as they would be if the process was run via the Datacap Studio. The process seems to perform the vscanmulti task but the result is just a vscanmulti.xml page file in the batch folder. The next task PageId obviously gets stuck as pending as no file was scanned. I tried using GrabBatch and Release but they just generate pagefiles in the Batch folder with the task names but no processing is performed. No task logs are produced either.
How do I get the app to process vscan then followed by the remaining tasks? I understand that I need to use the GetPageFile and SetPageFile but that is only after the scan is performed successfully.

The following are the steps:

1. /Session/Logon – successful
2. /Queue/CreateBatch – apparently successful. Request includes the pagefile definition.
3. /Queue/ReleaseBatch/AppDev/135/finished – successful
4. /Queue/GrabBatch/AppDev/135 – successful
5. /Queue/ReleaseBatch/AppDev/135/finished – successful
6. etc.

I have reviewed both the Knowledge Center and the IBM Datacap V9.0 Installing and Using Datacap Web Services.pdf as well as the Datacap-Web-Services-Projects sample from DeveloperWorks.
Thanks in advance.

Related:

Datacap Web Services Transaction/Start endpoint failing

I am attempting to use Datacap Web Services REST API methods to run a transaction call, similar to the transaction.java sample provided here: https://www.ibm.com/developerworks/data/library/techarticle/dm-1412datacap-developer-kit/DevWorks-Datacap-9.0-DDKwebservicess.html

Session/Logon is successful using the credentials supplied in Datacap Application Manager (wTMUser, wTMStation, wTMPassword).

Transaction/Start fails and returns the following value as the transactionId:
Sendera:BadRequestBad RequestThe connection to the application: , user: DOMAINsvc.acct, station: DCTM1 cannot be established.

The wtm log has similar error messages:
Error: Establish connection returned false for user DOMAINsvc.acct on station DCTM1 for application
Error: The connection to the application: , user: DOMAINsvc.acct, station: DCTM1 cannot be established.

In this error message, the application is empty, the user does not match wTMUser, and the station does not match wTMStation. However, DOMAINsvc.acct is the service account which runs Datacap Windows Service on the Taskmaster Server and DCTM1 is the computer name of the Taskmaster Server. DCTM1 is not a station that we have configured manually.

Datacap v9.1. Web Services running as a Windows Service. Queue endpoints work properly after Session/Logon.

Thanks for any feedback or suggestions.

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