WCF Service error: "This collection already contains an address with scheme http."

"This collection already contains an address with scheme http. There can be at most one address per scheme in this collection." is a Windows Communication Foundation (WCF) error message indicating you are trying to add an already existing binding. By default the web service listens to all host headers configured in IIS. A host header is the website address, for example example.com and www.example.com. If this is not correctly configured in the web.config file, WCF throws the error shown below.

Server Error in MultipleBindings Application

This collection already contains an address with scheme http. There can be at most one address per scheme in this collection.

With a correctly configured web.config it's quite possible to host the service on two URLs, for example https://payment.example.com:443 and https://payment.example.com:9000.

Fixes for "WCF Server Error in MultipleBindings Application" in different .NET Framework versions

Different .NET Framework versions have different solutions for this error.

Fix for .NET 2.0/3.0/3.5

1. Set a baseAddressPrefixFilters prefix for one of the two URLs in the web.config file:

<system.serviceModel>
  <serviceHostingEnvironment>
    <baseAddressPrefixFilters>
      <add prefix="https://payment.example.com:443"/>
    </baseAddressPrefixFilters>
  </serviceHostingEnvironment>
</system.serviceModel>

2. Add both endpoint URLs as absolute URLs in the web.config file:

<services>
  <service>
    <endpoint 
      address="https://payment.example.com:443/Service1.svc/EP1"
      binding="..."
      contract="..." />
    <endpoint address="https://payment.example.com:9000/Service1.svc/EP12"
      binding="..."
      contract="..." />
  </service>
</services>

Fix for ASP.NET 4.0/4.5

ASP.NET 4.0/4.5 has a multipleSiteBindingsEnabled web.config configuration option available, to support multiple site bindings for services. Keep this in mind when you port your 3.0/3.5 application to 4.0.

<serviceHostingEnvironment multipleSiteBindingsEnabled="true" />

For ASP.NET 4.0/4.5 you first must install the NET-HTTP-Activation and NET-WCF-HTTP-Activation features in IIS. Verify the *.svc handler is added to IIS after installation.

Is your service returning a 404 instead? Read why a .svc WCF web service returns 404 Not Found in IIS.

References and more information

• How can WCF support multiple IIS bindings specified per site? (MSDN blog, Wayback Machine)
• Supporting Multiple IIS Site Bindings on Microsoft Learn