Why am I getting a '401 Unauthorized' error with Easy Shipping Restrictions app?

[Carzan]

So we downloaded Easy Shipping Restrictions and get the following error message when the app is downloaded or we click on the app in Shopify Admin:

Fatal error: Uncaught GuzzleHttp\Exception\ClientException: Client error: `GET https://carzan-local-market.myshopify.com/admin/api/2022-01/recurring_application_charges.json` resulted in a `401 Unauthorized` response: {"errors":"[API] Invalid API key or access token (unrecognized login or wrong password)"} in /var/www/html/vendor/guzzlehttp/guzzle/src/Exception/RequestException.php:113 Stack trace: #0 /var/www/html/vendor/guzzlehttp/guzzle/src/Middleware.php(65): GuzzleHttp\Exception\RequestException::create(Object(GuzzleHttp\Psr7\Request), Object(GuzzleHttp\Psr7\Response)) #1 /var/www/html/vendor/guzzlehttp/promises/src/Promise.php(203): GuzzleHttp\Middleware::GuzzleHttp\{closure}(Object(GuzzleHttp\Psr7\Response)) #2 /var/www/html/vendor/guzzlehttp/promises/src/Promise.php(156): GuzzleHttp\Promise\Promise::callHandler(1, Object(GuzzleHttp\Psr7\Response), Array) #3 /var/www/html/vendor/guzzlehttp/promises/src/TaskQueue.php(47): GuzzleHttp\Promise\Promise::GuzzleHttp\Promise\{closure}() #4 /var/www/html/vendor/guzzlehttp/ in /var/www/html/vendor/guzzlehttp/guzzle/src/Exception/RequestException.php on line 113
There has been a critical error on your website.

I've deleted the app and reinstalled it numerous times and cannot get it to go away.

We've reached out to the developer through Shopify support, text and email and received no response for weeks.

So I come here to ask for help on how to fix this issue.

We need to restrict shipping by postal code so that no one outside the major city limits in each province can order, and it seems only this app will work for what we need.

Can anyone help?