Nested JSON array in REST request body

Hey @Matt . found the issue!

Solution:

we had to unselect:

  1. URL expects batch inserts

For Send new field values… we selected

  1. as templated request body

then went under custom request

  1. and added:
{
  "messages": [
    {
      "to": "{{to}}",
      "from": "{{from}}",
      "body": "{{body}}"
    }
  ]
}
saved and viola. it worked! 

The entire XML is: 
<skuidpage unsavedchangeswarning="yes" personalizationmode="server" showsidebar="false" useviewportmeta="true" showheader="false">
    <models>
        <model id="Send" query="false" createrowifnonefound="false" datasource="ClickSend" processonclient="true" type="readwrite" label="Message" labelplural="Messages">
            <fields>
                <field id="to" displaytype="TEXT" label="To" required="true" uionly="false"/>
                <field id="from" displaytype="TEXT" label="From" required="true" uionly="false"/>
                <field id="body" displaytype="TEXTAREA" label="Message" ogdisplaytype="TEXT" required="true" uionly="false"/>
                <field id="custom_string" displaytype="TEXT" label="Patient Case ID" uionly="false"/>
            </fields>
            <conditions/>
            <actions/>
            <methods>
                <method type="insert" verb="POST" successif="responsefieldequals" sendchanges="usetemplaterequest" endpoint="/sms/send" batch="false" successfield="response_code" contenttype="application/json" payloadsnippet="cs_snip" insertresponse="recordinbody" customrequesttemplate="{&#10;  &quot;messages&quot;: [&#10;    {&#10;      &quot;to&quot;: &quot;{{to}}&quot;,&#10;      &quot;from&quot;: &quot;{{from}}&quot;,&#10;      &quot;body&quot;: &quot;{{body}}&quot;&#10;    }&#10;  ]&#10;}"/>
            </methods>
        </model>
    </models>
    <components>
        <buttonset model="Send" uniqueid="sk-3PATUJ-218">
            <buttons>
                <button type="multi" label="New Message" uniqueid="sk-3PATl0-221" icon="sk-icon-add">
                    <actions>
                        <action type="createRow" model="Send" appendorprepend="prepend" defaultmodefornewitems="edit" affectedrows="context"/>
                    </actions>
                </button>
            </buttons>
        </buttonset>
        <basicfieldeditor showheader="true" showsavecancel="true" showerrorsinline="true" model="Send" uniqueid="sk-3PALtc-174" mode="edit">
            <columns>
                <column width="100%">
                    <sections>
                        <section title="Section A" collapsible="no">
                            <fields>
                                <field uniqueid="sk-3PAOCB-189" id="to"/>
                                <field uniqueid="sk-3PARw5-200" id="from" valuehalign="" type=""/>
                                <field uniqueid="sk-3PASIg-209" id="body" valuehalign="" type=""/>
                                <field uniqueid="sk-3PIMR1-537" id="custom_string" valuehalign="" type="">
                                    <label>Case ID</label>
                                </field>
                            </fields>
                        </section>
                    </sections>
                </column>
            </columns>
        </basicfieldeditor>
    </components>
    <resources>
        <labels/>
        <javascript>
        </javascript>
        <css/>
        <actionsequences/>
    </resources>
    <styles>
        <styleitem type="background" bgtype="none"/>
    </styles>
</skuidpage>

let me know if this helps.