Redmine

Hello,
I try to create one anonymous request via API REST and I get the following error:

Parameters: {"issue"=>{"project_id"=>"anonymoususerserviceoperations", "tracker_id"=>"4", "subject"=>"Support Service", "description"=>"How do I create one User Service Request ?", "status_id"=>"1", "category"=>"1", "custom_fields"=>[{"id"=>"11", "name"=>"User contact", "value"=>"anonymous@company.fr"}]}}
Current user: anonymous
Filter chain halted as :find_optional_project rendered or redirected

My request is :

<?xml version="1.0" encoding="ISO-8859-1" ?>
<issue>
  <project_id>anonymoususerserviceoperations</project_id>
  <tracker_id>4</tracker_id>
  <subject>Support Service</subject>
  <description>How do I create one User Service Request ?</description>
  <status_id>1</status_id>
  <category>1</category>
  <!--<assigned_to id="6" name="FrontDeskEngineer"/>-->
  <custom_fields type="array">
      <custom_field id="11" name="User contact">
        <value>anonymous@company.fr</value>
      </custom_field>
  </custom_fields>
</issue>

Thank you for your help
Katie