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<h1>REST Service Error: 503 Service Unavailable (Tenant Under Maintenance)</h1>
<div class="trix-content"><p><strong>Description</strong></p><p>This error occurs when a REST API call to a service receives an HTTP status code outside the 20x (success) range, indicating the request was not processed successfully.<br><br></p><p><code>The REST service returned a status code that is not 20x - i.e. not OK - Status code received: 503 Service Unavailable Response body: {"error": {"code": "Upgrade","message": "Tenant under maintenance. Maintenance type: Upgrade"}}</code></p><p><strong>Error Details</strong></p><ul><li><strong>Status Code:</strong> 503 Service Unavailable</li><li><strong>Error Code:</strong> <code>Upgrade</code></li><li><strong>Message:</strong> "Tenant under maintenance. Maintenance type: Upgrade"</li></ul><p><strong>Cause</strong></p><p>The target tenant (commonly a Business Central or Dynamics 365 environment) is temporarily unavailable because it is undergoing a scheduled or in-progress upgrade. During this maintenance window, the tenant's API endpoints reject incoming requests to prevent data inconsistency.</p><p><strong>Resolution</strong></p><ul><li>Wait for the maintenance/upgrade to complete before retrying the request.</li><li>Implement retry logic with exponential backoff for integration jobs that may run during maintenance windows.</li><li>Check the tenant's admin center or service status page for an estimated maintenance completion time.</li><li>If the issue persists beyond the expected maintenance window, contact the tenant administrator or platform support.</li></ul></div>
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