Certificate HTTPS could not create SSL relationship trust vb.net

Question

I am consistently getting this error:

Could not establish trust relationship for the SSL/TLS secure channel with authority 'dev1sintiaweb01'.

I am sure, I had signed the certificate. Why do I still get this error? What can I do to fix it?

This is my Server WebConfig.

<?xml version="1.0" encoding="UTF-8"?>

<configuration>
  <configSections>
    <sectionGroup name="applicationSettings" type="System.Configuration.ApplicationSettingsGroup, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089">
      <section name="SpasiWebService.My.MySettings" type="System.Configuration.ClientSettingsSection, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
    </sectionGroup>
  </configSections>
  <appSettings />
  
  <system.web>
    <compilation debug="true" strict="false" explicit="true" targetFramework="4.6.1">
            
        </compilation>
    <httpRuntime />
    <pages controlRenderingCompatibilityVersion="4.0" />
  </system.web>
  <system.serviceModel>
    <services>  
        <service name="SpasiService.IService1">  
        <endpoint address="basic" binding="basicHttpsBinding" contract="SpasiService.IService1" />    
        </service>  
    </services> 
    <bindings>
            <basicHttpsBinding>
                <binding maxBufferPoolSize="2147483647" maxBufferSize="2147483647" maxReceivedMessageSize="2147483647" transferMode="Streamed" >
                    <readerQuotas maxDepth="2147483647" maxStringContentLength="2147483647" maxArrayLength="2147483647" maxBytesPerRead="2147483647" maxNameTableCharCount="2147483647" />
                </binding>
            </basicHttpsBinding>
        </bindings>

    <behaviors>
      <serviceBehaviors>
        <behavior>
         <serviceMetadata httpGetEnabled="true" httpsGetEnabled="true"/>
         <serviceDebug includeExceptionDetailInFaults="false"/>
        </behavior>
      </serviceBehaviors>
    </behaviors>
    <protocolMapping>
      <add binding="basicHttpsBinding" scheme="https" />
    </protocolMapping>
    <serviceHostingEnvironment aspNetCompatibilityEnabled="true" multipleSiteBindingsEnabled="true" />
  </system.serviceModel>
  <system.webServer>
    <modules runAllManagedModulesForAllRequests="true" />
   
    <directoryBrowse enabled="true" />
  </system.webServer>
  
</configuration>

This is My Client AppConfig.

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <configSections>
    <sectionGroup name="userSettings" type="System.Configuration.UserSettingsGroup, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089">
      <section name="DosirAsli.My.MySettings"
        type="System.Configuration.ClientSettingsSection, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
        allowExeDefinition="MachineToLocalUser" requirePermission="false"/>
    </sectionGroup>
  <!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 -->
  <section name="entityFramework"
      type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
      requirePermission="false"/>
  </configSections>
  <startup>
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.6"/>
  </startup>
  <userSettings>
    <DosirAsli.My.MySettings>
      <setting name="strLinkMyBCA" serializeAs="String">
        <value>https://mybcaportal/sites/ai/Aplikasi Pengawasan Internal/</value>
      </setting>
    </DosirAsli.My.MySettings>
  </userSettings>
  <entityFramework>
    <providers>
      <provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer"/>
      <provider invariantName="System.Data.SQLite.EF6" type="System.Data.SQLite.EF6.SQLiteProviderServices, System.Data.SQLite.EF6"/>
    </providers>
  </entityFramework>

  <system.net>
    <settings>
      <servicePointManager checkCertificateName="false" checkCertificateRevocationList="false" />
    </settings>
  </system.net>
  
  <system.serviceModel>
    <bindings>
      <basicHttpsBinding>
        <binding name="BasicHttpsBinding_IService1" maxBufferPoolSize="2147483647" maxBufferSize="2147483647" maxReceivedMessageSize="2147483647" >
          <readerQuotas maxDepth="2147483647" maxStringContentLength="2147483647" maxArrayLength="2147483647" maxBytesPerRead="2147483647" maxNameTableCharCount="2147483647" />
          <security mode="Transport">
            <transport clientCredentialType="Ntlm" />
          </security>

        </binding>
      </basicHttpsBinding>
     
    </bindings>
    
    <!--<client>
      
    </client>-->

    <client>
  
      <endpoint address="https://dev1sintiaweb01/WebServiceSpasi/Service1.svc"
        binding="basicHttpsBinding" bindingConfiguration="BasicHttpsBinding_IService1"
        contract="SpasiWebService.IService1" name="BasicHttpsBinding_IService" />
    </client>

  </system.serviceModel>


</configuration>

Error Stack Trace

Server stack trace:     at
System.ServiceModel.Channels.HttpChannelUtilities.ProcessGetResponseWebException(WebException
webException, HttpWebRequest request, HttpAbortReason abortReason)   
at
System.ServiceModel.Channels.HttpChannelFactory`1.HttpRequestChannel.HttpChannelRequest.WaitForReply(TimeSpan
timeout)    at
System.ServiceModel.Channels.RequestChannel.Request(Message message,
TimeSpan timeout)    at
System.ServiceModel.Dispatcher.RequestChannelBinder.Request(Message
message, TimeSpan timeout)    at
System.ServiceModel.Channels.ServiceChannel.Call(String action,
Boolean oneway, ProxyOperationRuntime operation, Object[] ins,
Object[] outs, TimeSpan timeout)    at
System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(IMethodCallMessage
methodCall, ProxyOperationRuntime operation)    at
System.ServiceModel.Channels.ServiceChannelProxy.Invoke(IMessage
message)

Exception rethrown at [0]:     at
System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage
reqMsg, IMessage retMsg)    at
System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData&
msgData, Int32 type)    at
DosirAsli.SpasiWebService.IService1.CekDomainTersedia(String
strDomain)    at
DosirAsli.SpasiWebService.Service1Client.CekDomainTersedia(String
strDomain) in E:\Project CAAT\Web
PI\Web_PI\WebPI-DevBranch\DosirAsli\Connected
Services\SpasiWebService\Reference.vb:line 96    at
DosirAsli.Login.btnLogin_Click(Object sender, EventArgs e) in
E:\Project CAAT\Web PI\Web_PI\WebPI-DevBranch\DosirAsli\Login.vb:line
43