Eloquent model returns 0 as primary key

You can also set the type of primary key:

protected $keyType = 'string';
public $incrementing = false;

Important note. You should add the second line. $incrementing = false. If you do not this, the key will be 0 after calling save() on your model.

You can try setting public $incrementing = false; on your model so eloquent doesn't expect your primary key to be an autoincrement primary key.