Composer require Error

Quando executo o comando:

```
composer require prettus/moip-assinaturas-laravel
```

tenho como resposta um erro:

```
[InvalidArgumentException]
Could not find package prettus/moip-assinaturas-laravel at any version for your minimum-stability (stable). Check the package spelling or your mi
nimum-stability
```

ainda tentei colocar dentro do composer.json e executar `composer update`, gerando outro erro:

```
Your requirements could not be resolved to an installable set of packages.

Problem 1
- Installation request for prettus/moip-assinaturas-laravel dev-master -> satisfiable by prettus/moip-assinaturas-laravel[dev-master].
- prettus/moip-assinaturas-laravel dev-master requires prettus/moip-assinaturas-php dev-master -> no matching package found.

Potential causes:
- A typo in the package name
- The package is not available in a stable-enough version according to your minimum-stability setting
see for more details.

Read for further common problems.
```

Está parecendo que ele não encontra o plugin no packagist, pelo menos nenhuma versão estável.