Zedd I'm getting the same error. Eventually managed to install it with
composer require katosdev/signature:*
But now I'm on 1.1.3 version and can't update it on 1.2
When I try with : composer update katosdev/signature:2.1 -W
I'm getting this error
Problem 1
- Root composer.json requires katosdev/signature *, 2.1, found katosdev/signature[dev-master, 1.0.0, ..., 1.2] but it does not match the constraint.