406 Not Applicable on Post Order by Ian Stull

I'm successfully posting orders, but still receiving a 406 response which is causing exceptions on my end. My XML to be posted takes this form:

<?xml version="1.0" encoding="utf-8"?>
<order>
     <financial_status>pending</financial_status>
     <line-items type="array">
          <line-item>
               <variant_id type="integer">585339453</variant_id>
               <quantity>1</quantity>
          </line-item>
          <line-item>
               <variant_id type="integer">585339329</variant_id>
               <quantity>1</quantity>
          </line-item>
      </line-items>
      <customer>
          <id type="integer">234280725</id>
      </customer>
</order>

Which successfully posts the order, but gets a 406 (Not Acceptable) response. Any help would be appreciated. It's the last step in a major project.