PUT request with COBOL

My including the word COBOL in the subject header might well be misleading, as in reality, my question could be relevant for whatever language is handling the PUT request. Anyway here goes.

I’m a newbie to Postman. I have defined collections in Postman with GET requests such that the actual request becomes something like
MYURL/?account_number=123456
then sent in the request and picked it up via a EXEC CICS WEB READ call. All well and good, I get the value 123456 into my variable in my COBOL program.

Now I need to do the same thing with a PUT request, where the COBOL program will read the data via an EXEC CICS GET CONTAINER, i.e., read a whole block of data in one go and where the data read corresponds to a COBOL copybook. For example, the first 10 bytes might represent a date, the next 25 a customer name etc.
My question is, how do I define these fields in Postman (remembering that there might be 40, 50 or many more of them).
I found the following link

Is this the best way to go? I imagine the CSV variation is simple, if one was to define the data in Excel and then save the spreadsheet as a CSV file. Having said that, if I define 2 rows in Excel, save them as a CSV file and use them in Postman, would 2 requests be sent automatically?

I tried following the instructions in the URL above. I created a simple CSV file on my desktop and selected it in Runner, but I received the error message

Couldn’t upload file. Make sure that Postman can read files inside the working directory

Is that me doing something wrong or the instructions in the URL above missing something ?
I also tried downloading the sample collection and data file mentioned in the URL and saving them on my desktop and then loading that, but that failed as well.
I’ll stop here on the assumption that I’m doing something wrong.
Thanks you

Oh, and by the way, if you try and run the Select File more than once with the same (refused) file, the second (and following times) you select the file you get NO “Couldn’t upload file” message.
That would seem to be an error to me (making me think that the second time the file was selected successfully)

Tried again from work where it worked nicely. Could it be that the failing one is using the client version of Postman (installed at home where it failed) and the successful one is using the “full-blown” version at work?

Since this is all completely new to me, I’ll append a number of questions, all relating to a PUT request and to the samples from the URL above.
So, the URL in the SAMPLE example is

postman-echo.com/{{path}}

and the sample data file contains variations on

{
	"path": "post",
	"value": "1"
},

How does the URL tie in with the sample data. Is the value “path” in the URL replaced by the text (request) POST?
What happens if I have multiple values to be sent in; how do I specify the “value” parms for more than 1 value for the same request.
Can I “import” the values and place them in the Tests settings as shown here

(or should this be placed in the Body part) rather than having to refer to the external file every time I want to run the test request.

Thank you