Unable to establish connection to Shopify

We’ve setup the private Shopify app and input all of the secret and authentication keys into the WordPress plugin settings. When attempting to connect, the initial sync screen loads and is never able to establish a connection. It hangs on the syncing screen indefinitely with no progress beyond “Preparing Shopify Connection…”

There are a number of preflight and authentication errors from the console:

[Error] Preflight response is not successful
[Error] XMLHttpRequest cannot load https://XXXXXXXXXXX.net/wp-json/wpshopify/v1/license/ due to access control checks.
[Error] Failed to load resource: Preflight response is not successful (license, line 0)
[Error] Unhandled Promise Rejection: TypeError: undefined is not an object (evaluating 'e.status')
	Wa (admin.08ddc92c.min.js:1:76785)
	(anonymous function) (admin.08ddc92c.min.js:1:79922)
	promiseReactionJob
[Error] Preflight response is not successful
[Error] XMLHttpRequest cannot load https://XXXXXXXXXXX.net/wp-json/wpshopify/v1/syncing/notices/ due to access control checks.
[Error] Failed to load resource: Preflight response is not successful (notices, line 0)
[Error] Unhandled Promise Rejection: TypeError: undefined is not an object (evaluating 'e.status')
	Wa (admin.08ddc92c.min.js:1:76785)
	(anonymous function) (admin.08ddc92c.min.js:1:79922)
	promiseReactionJob
[Error] Preflight response is not successful
[Error] XMLHttpRequest cannot load https://XXXXXXXXXXX.net/wp-json/wpshopify/v1/cache/ due to access control checks.
[Error] Failed to load resource: Preflight response is not successful (cache, line 0)
[Error] Unhandled Promise Rejection: TypeError: undefined is not an object (evaluating 'e.status')
	Wa (admin.08ddc92c.min.js:1:76785)
	(anonymous function) (admin.08ddc92c.min.js:1:79922)
	promiseReactionJob
[Error] Preflight response is not successful
[Error] XMLHttpRequest cannot load https://XXXXXXXXXXX.net/wp-json/wpshopify/v1/notices/ due to access control checks.
[Error] Failed to load resource: Preflight response is not successful (notices, line 0)
[Error] Unhandled Promise Rejection: TypeError: undefined is not an object (evaluating 'e.status')
	Wa (admin.08ddc92c.min.js:1:76785)
	(anonymous function) (admin.08ddc92c.min.js:1:79922)
	promiseReactionJob

Any thoughts on what may be happening here? Is the REST API access blocked? Thanks in advance for any information you can provide.