Hello @nehalkapadiya,

There are multiple ways to do this:

One way is checking the releases on GitHub to find where the support for Laravel 6 is dropped.

Another way is to check the blame on composer.json to see when the requirement is changed.

The third (and my preferred) option is checking the packagist page for the package and check the versions to see support for the illuminate 6 versions.

For all the options it helps to know that the support of an older Laravel version is a BC break that results in a new major version. In this case it means that because the 13.* doesn't work I should check the latest 12.* version. That is 12.15.0 en packagist say that is working. See: https://packagist.org/packages/laravel/cashier#v12.15.0

So you can run composer require laravel/cashier:^12.0 to get the wanted version.