composer does not find branch in forked repository

At work I forked the git repository of a TYPO3 extension, created a branch and tried to install it in my project - but composer failed to find it.

At first I added a repositories section with my forked github repo as vcs repository:

"repositories": [
    {
        "type": "vcs",
        "url": "https://github.com/mogic-le/aus_driver_amazon_s3"
    }
],

Then I tried to install my branch:

$ composer require andersundsehr/aus-driver-amazon-s3:dev-mogic-v13
./composer.json has been updated
Running composer update andersundsehr/aus-driver-amazon-s3
Loading composer repositories with package information
Updating dependencies
Your requirements could not be resolved to an installable set of packages.
 
  Problem 1
    - Root composer.json requires andersundsehr/aus-driver-amazon-s3 dev-mogic-v13, found andersundsehr/aus-driver-amazon-s3[dev-feature/unbundle-sdk, dev-feature/matrix-tests, dev-functional-tests-alternative, dev-task/fixTests, dev-master, dev-TYPO3v13, dev-bugfix/clear-transient-file, 1.3.2, ..., 1.13.5, 2.0.0] but it does not match the constraint.
 
 
Installation failed, reverting ./composer.json to its original content.

After half an hour I finally found the reason:

$ composer validate
./composer.json is valid, but with a few warnings
See https://getcomposer.org/doc/04-schema.md for details on the schema
# General warnings
- Key repositories is a duplicate in ./composer.json at line 68

My composer.json already had a "repositories" section at the end, but I added a new section near the beginning. The section at the end overwrote the one at the beginning, and so composer never saw my custom repository.

Written by Christian Weiske.

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