How do I install a plugin after buying it?

After purchase you receive credentials for the private Composer repository: the email address on your license and your license key.

composer config repositories.qalainau composer https://qalainau.privato.pub/composer
composer config --auth http-basic.qalainau.privato.pub "your-email" "your-license-key"
composer require qalainau/filament-warp-table
php artisan filament:assets

Use the same credentials on every machine that installs the package, such as your laptop, CI and production. Keep auth.json out of Git, and on CI or servers pass the credentials in the COMPOSER_AUTH environment variable instead.

Never post your license key here. Add your license on your account page: it shows these commands with your email filled in, and gives your questions the Customer badge. The key is checked and not stored.