Change the composer require

[MortalKonga]

composer require augusthur/php-firmar
Returns the following:

Could not find a matching version of package augusthur/php-firmar. Check the package spelling, your version constraint and that the package is available in a stability which matches your minimum-stability (stable).

It should be changed to
composer require augusthur/firmar-php

[MortalKonga]

I just checked in packagist and it should be changed there too.