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I have entered the User ID and the Password, but the Response shows that the Site ID is incorrect:
<ActionStatus>Error</ActionStatus> <Condition> <ConditionCode>100</ConditionCode> <ConditionData>Validation Failure:Site Id is wrong</ConditionData>
The credentials (SITE ID and PASSWORD) that you are using are Test credentials. That is why you are getting the error, as you are trying to use them in live mode.
For the test mode, the production key should be unchecked.
Getting SiteID and password for countries other than the United States (UK and Rest of the world) for the live mode:
The customer should contact DHL account manager. The account manager must request integration with ELEX via DHL Pre-sales department.
Pre-sales team will then provide the customer with live credentials.
To explore more details about the plugins, go check out ELEX WooCommerce DHL Express / eCommerce / Paket Shipping Plugin with Print Label.
You can also check out other WooCommerce and WordPress plugins in ELEX.