If your WHMCS installation suddenly stops working, throws a license error, or refuses to validate after enabling IPv6, it may be due to a known issue with dual stack environments (servers using both IPv4 and IPv6).
The Problem
WHMCS licenses are typically tied to your server’s IP address. On modern servers configured with both IPv4 and IPv6 (dual stack), some services—including licensing calls—may route over IPv6 by default. If your license was only registered to your IPv4 address, this causes a mismatch and results in license validation failure.
You might experience:
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License not found or invalid
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WHMCS admin area locked out
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Error messages referencing IP mismatches
The Solution
Contact WHMCS support and request that your license be updated to support dual stack IP environments. This is a common request, and they can update the license on their end to recognize both the IPv4 and IPv6 addresses associated with your server.
Steps to resolve:
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Log in to your WHMCS client area or open a support ticket.
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Provide both your server’s IPv4 and IPv6 addresses.
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Mention that you’re experiencing issues due to dual stack configuration.
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Ask them to update the license to support both IP versions.
Once the license is updated, WHMCS should function normally again—no need to disable IPv6.
Pro Tip
This issue often arises after:
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Enabling IPv6 on your server
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Migrating to a host with dual stack networking
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WHMCS making outbound requests over IPv6 instead of IPv4
To avoid future disruptions, make sure your license is updated anytime your server's IPs change.
