Soap API - 500 Internal Server Error

I have a legacy app that was working, but is now failing with the SOAP api.

Since I don't have time to re-code for the REST api immediately, so have to get this working for now.

Currently try to get test sendDocument via SoapUI, and just getting a 501 response from the server, with an error message that means nothing useful to me.

Anyone have any idea what's breaking it here?

This should be the minimum required data (with some things anonymized), if I leave anything else out it gives an appropriate error:

Test Data:

https://secure.na1.echosign.com/services/EchoSignDocumentService22

Request:

<soapenv:Envelope

  xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/"

  xmlns:api="http://api.echosign"

  xmlns:dto="http://dto.api.echosign"

  xmlns:dto2="http://dto21.api.echosign"

  xmlns:dto9="http://dto9.api.echosign"

  xmlns:dto21="http://dto20.api.echosign"

  xmlns:dto1="http://dto14.api.echosign"

  xmlns:dto11="http://dto18.api.echosign"

  xmlns:dto12="http://dto19.api.echosign"

  >

   <soapenv:Header/>

   <soapenv:Body>

      <api:sendDocument>

         <api:apiKey>###MY API KEY###</api:apiKey>

         <api:senderInfo>

            <dto:userKey>###MY USER KEY###</dto:userKey>

         </api:senderInfo>

         <api:documentCreationInfo>

            <dto:fileInfos>

               <dto:FileInfo>

                  <dto:fileName>123456.pdf</dto:fileName>

                  <dto:url>###URL TO SAMPLE PDF FILE###</dto:url>

               </dto:FileInfo>

            </dto:fileInfos>

            <dto:message>I am a potato.</dto:message>

            <dto:name>TEST</dto:name>

            <dto:recipients>

               <dto1:RecipientInfo>

                  <dto1:email>###MY EMAIL###</dto1:email>

                  <dto1:role>SIGNER</dto1:role>

               </dto1:RecipientInfo>

            </dto:recipients>

         </api:documentCreationInfo>

      </api:sendDocument>

   </soapenv:Body>

</soapenv:Envelope>

Response is:

HTTP/1.1 500 Internal Server Error

Date: Sun, 23 Sep 2018 23:25:11 GMT

Server: Apache

Strict-Transport-Security: max-age=31536000;

X-XSS-Protection: 1; mode=block

X-Content-Type-Options: nosniff

X-Robots-Tag: none

P3P: CP="IDC DSP COR ADM DEVi TAIi PSA PSD IVAi IVDi CONi HIS OUR IND CNT"

Connection: close

Transfer-Encoding: chunked

Content-Type: text/xml;charset=UTF-8

<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

   <soap:Body>

      <soap:Fault>

         <faultcode>soap:Server</faultcode>

         <faultstring>apiActionId=CBJCHBCAABAAo0scmCeb0bkMBa1XTJwKn0XH0FHaz5y8</faultstring>

      </soap:Fault>

   </soap:Body>

</soap:Envelope>

-Phil