Checksum error on manual package install

[Lorem Ipsum]

Hi,

I am trying to install a non-packaged piece of software, [[
https://nomacs.org/][nomacs]].  It
seems that through the paradigm of Guix, this is to be done with ~guix
package~ rather than with ~make~ etc.  Or, put differently, to install
an application which is not in the package repos, I need to package it
myself.  Am I correct in my understanding?

I have read through "[[
https://www.gnu.org/software/guix/manual/en/html_node/Defining-Packages.html][Section
6.2 Defining Packages]]", as well as the
blog post "[[
https://www.gnu.org/software/guix/blog/2018/a-packaging-tutorial-for-guix/][A
packaging tutorial for Guix]]", and followed along at home.
I was successful in packaging and installing "my-hello.scm".  It seems
to me that packaging ~nomacs~ should be as simple as replacing the
relevant pieces within the "my-hello.scm" template.

#+begin_src scheme :file my-nomacs.scm
(use-modules (guix packages)
         (guix download)
         (guix build-system gnu)
         (guix licenses))

(package
   (name "nomacs")
   (version "3.12")
   (source (origin
        (method url-fetch)
        (uri (string-append "https://github.com/nomacs/nomacs/archive/";
version
                ".tar.gz"))
        (sha256
         (base32

"f4a32169e6c0cb939971da2732e4d67c6e2e649506da1b55bfc94963a26280ff"))))
   (build-system gnu-build-system)
   (synopsis "Open source image viewer")
   (description
    "nomacs is a free, open source image viewer, which supports
multiple platforms. You can use it for viewing all common image
formats including RAW and psd images.")
   (home-page "https://nomacs.org";)
   (license gpl3+))
#+end_src

However, when I try to install, I get an error about invalid base32:
#+begin_src sh
$ guix package --install-from-file=my-nomacs.scm

guix package: error: exception thrown: #<condition
&invalid-base32-character [character: #\e string:
"f4a32169e6c0cb939971da2732e4d67c6e2e649506da1b55bfc94963a26280ff"]
23ee2a0>
#+end_src

Here is how I obtained that hash:
#+begin_src sh
$ wget https://github.com/nomacs/nomacs/archive/3.12.tar.gz
--2019-07-02 06:36:39--
https://github.com/nomacs/nomacs/archive/3.12.tar.gz
Resolving github.com (github.com)... 192.30.253.112
Connecting to github.com (github.com)|192.30.253.112|:443... connected.
HTTP request sent, awaiting response... 302 Found
Location: https://codeload.github.com/nomacs/nomacs/tar.gz/3.12 [following]
--2019-07-02 06:36:40--
https://codeload.github.com/nomacs/nomacs/tar.gz/3.12
Resolving codeload.github.com (codeload.github.com)... 140.82.113.9
Connecting to codeload.github.com (codeload.github.com)|140.82.113.9|:443...
connected.
HTTP request sent, awaiting response... 200 OK
Length: unspecified [application/x-gzip]
Saving to: ‘3.12.tar.gz.1’

3.12.tar.gz.1           [    <=>             ]   1.66M  2.54MB/s    in 0.7s

2019-07-02 06:36:41 (2.54 MB/s) - ‘3.12.tar.gz.1’ saved [1736648]

$ sha256sum 3.12.tar.gz
f4a32169e6c0cb939971da2732e4d67c6e2e649506da1b55bfc94963a26280ff
3.12.tar.gz
#+end_src

This is where I'm stuck.  I know that the hash needs to be base32 and
that the hash returned by ~sha256sum~ is not that.  I would think this
wouldn't matter since the Guile script calls ~base32~.

I'm unsure how to proceed.  Any advice would be appreciated!

Thank you,
Matt