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After granting the permission to the Apex class, you wll need to grant access to site guest user for the Xero-related objects
From the Site Guest user profile page, navigate to the Custom Object Permission & Standard Object Permission section and grant read permission for the following objects.
Grant field level access to the fields of the objects.
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In the Custom URLs section, click on the Preview as Admin link on the HTTPS version. This will be shown with “Salesforce Sites Subdomain”.
The page that opens will be the Site URL you need to copy.
For example, the URL that we need to note is “https://twixrivademo-developer-edition.um6.force.com/ ”
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