WP JSON API URLs don't work on sub-directory multisite

[kasparsd]

Describe the bug
When attempting to use the plugin on a subdomain multisite site such as example.com/site-one, the REST API URLs in all JS files point to the root site example.com/wp-json/... instead of example.com/site-one/wp-json/....

To Reproduce
Steps to reproduce the behavior:

1. Go to plugin settings page.
2. Click on "Connect to Lemon Squeezy"
3. Accept the connection and get redirected back to the site.
4. Notice that the site is still not connected -- the same "Connect to" button is shown.

Expected behavior
Site can be connected to Lemon Squeeze when used from WP sub-directory multisite.

Screenshots

Software (please complete the following information):

• Plugin version: 1.3.0
• WordPress version: 6.6.2
• PHP version: 7.4
• Browser: Safari and Chrome

Additional context

[kasparsd]

The issue is caused by the hardcoded REST API paths in all JS files such as:

lemonsqueezy-wp/src/admin/admin.js

Line 124 in b571124

return fetch("/wp-json/lsq/v1/validate")

Using the @wordpress/api-fetch library for sending the REST API requests automatically takes care of using the correct site URL.