You can try to do it using the OpenSSL libraries, which comes complete with Caché/Ensemble/etc.
To google: "openssl rsa-pss sign", "openssl SHA256 with RSA PSS padding"

Here is a small example on Windows, where it is assumed that

• cert.pem is your certificate:
  

  -----BEGIN CERTIFICATE-----
  <...>
  -----END CERTIFICATE-----

• key.pem is your private key:
  

  -----BEGIN RSA PRIVATE KEY-----
  <...>
  -----END RSA PRIVATE KEY-----

So (test.bat):

@echo off
 
echo Delete all temporary files
del /Q /F test.txt test.sig pubkey.pem test.b64
 
echo Extract the public key from certificate (only be done once)
openssl x509 -pubkey -in cert.pem -noout > pubkey.pem
 
echo Create test file (test.txt)
echo bla-bla-bla test123 {Date}{newline}{Password}{newline}{etc}{Message Body} > test.txt
 
echo Create signature (test.sig)
openssl dgst -sha256 -sigopt rsa_padding_mode:pss -sigopt rsa_pss_saltlen:-1 -sign key.pem -out test.sig test.txt
 
echo This step is only for information/verification.
echo Verify signature (The result should be: "Verified OK")
openssl dgst -sha256 -sigopt rsa_padding_mode:pss -sigopt rsa_pss_saltlen:-1 -signature test.sig -verify pubkey.pem test.txt
 
echo Convert signature to Base64 (test.b64)
echo You can this step be make on COS.
openssl base64 -in test.sig -out test.b64 -nopad

Or on COS:

#include %systemInclude
#include %occErrors
main() public {
  
  s fileMsg="test.txt",
    fileSig="test.sig",
    file64="test.b64",
    filePubKey="pubkey.pem",
    fileCert="C:\SSL\cert.pem",
    fileKey="C:\SSL\key.pem"

  try {
    $$$AddAllRoleTemporaryInTry
    n $namespace


    if '##class(%File).Exists(filePubKey) {
      ; Only be done once
      ; Extract the public key from certificate
      s cmd=$$$FormatText("openssl x509 -pubkey -in %1 -noout > %2",fileCert,filePubKey)
      w cmd,!!
      d $zf(-1,cmd)
    }
    
    f i=fileMsg,fileSig,file64 d ##class(%File).Delete(i)
    
    s file=##class(%Stream.FileCharacter).%New()
    s file.Filename=fileMsg
    s file.TranslateTable="UTF8"
    d file.WriteLine("{Date}")
    d file.WriteLine("{Password}")
    d file.Write("{etc}{Message Body}")
    $$$ThrowOnError(file.%Save())
    
    w $$$FormatText("Create signature (%1)",fileSig),!
    s cmd=$$$FormatText("openssl dgst -sha256 -sigopt rsa_padding_mode:pss -sigopt rsa_pss_saltlen:-1 -sign %1 -out %2 %3",fileKey,fileSig,fileMsg)
    w cmd,!!
    d $zf(-1,cmd)
    
    w $$$FormatText("Convert signature to Base64 (%1)",file64),!
    s cmd=$$$FormatText("openssl base64 -in %1 -out %2 -nopad",fileSig,file64)
    w cmd,!!
    d $zf(-1,cmd)
    
    ;here we read our file test.b64 (file64) and place it in a Signature field in the header
    
  }catch(ex) {
    w "Error ", ex.DisplayString(),!
  }

  f i=fileMsg,fileSig d ##class(%File).Delete(i)
}

It seems that "CREATE TRIGGER" does not support INSERT/UPDATE, INSERT/UPDATE/DELETE, etc.
It's either a bug or a feature. I believe that is still a bug.
In any case you need to contact the WRC.

Could the issue be something with the dataBinding?

Most likely - yes, see <dataController> Methods.
Simple example:

Class demo.relationModel Extends %ZEN.DataModel.ObjectDataModel
{

Property Relation As %String(MAXLEN = 36);

Method %OnLoadModel(pSource As %RegisteredObject) As %Status
{
  s ..Relation = $g(^tmp,"BLACKFIN CAPITAL PARTNERS")
  q $$$OK
}

Method %OnStoreModel(pSource As %RegisteredObject) As %Status
{
  k ^tmp
  s ^tmp=..Relation
  q $$$OK
}
}

Class demo.test Extends %ZEN.Component.page
{

XData Contents [ XMLNamespace = "http://www.intersystems.com/zen" ]
{
<page xmlns="http://www.intersystems.com/zen" title="">
  <dataController
    id="relationData"
    modelClass="demo.relationModel"
  />
  <form
    id="MyForm"
    controllerId="relationData"
  >
    <text
      id="Relation"
      label="Relation"
      name="Relation"
      dataBinding="Relation"
      size="36"
    />
    <button caption="1. Convert" onclick="zenPage.convertToTitle();"/>
    <button caption="2. Save" onclick="zen('MyForm').save();" />
  </form>
</page>
}

ClientMethod convertToTitle() [ Language = javascript ]
{
  var controller = zen('relationData');
  
  controller.setDataByName('Relation',this.stringConvert(zen('Relation').getValue()));
  controller.raiseDataChange();
}

ClientMethod stringConvert(str) [ Language = javascript ]
{
  ///alert (str)
  str = str.substring(0,1).toLowerCase() + str.substring(1).toLowerCase();
  ///alert (str)
  var pieces = str.split(" ");
  for ( var i = 0; i < pieces.length; i++ )
  {
    var j = pieces[i].charAt(0).toUpperCase();
    
    pieces[i] = j + pieces[i].substr(1);
  }
      
  return pieces.join(" ");
}
}

At me converted string is stored correctly.

Here is a small example:

Class demo.test Extends %ZEN.Component.page
{

XData Contents [ XMLNamespace = "http://www.intersystems.com/zen" ]
{
<page xmlns="http://www.intersystems.com/zen" title="">
  <form
    id="MyForm"
    OnLoadForm="LoadForm"
    OnSubmitForm="SubmitForm"
  >
    <text
      id="Relation"
      name="Relation"
      label="Relation"
      size="50"
    />
    <button caption="1.Convert" onclick="zenPage.convertToTitle();"/>
    <submit caption="2.Save" action="save"/>
  </form>
</page>
}

ClientMethod convertToTitle() [ Language = javascript ]
{
  var ctrl = zen('Relation');
  ctrl.setValue(this.stringConvert(ctrl.getValue()));
}

ClientMethod stringConvert(str) [ Language = javascript ]
{
  ///alert (str)
  str = str.substring(0,1).toLowerCase() + str.substring(1).toLowerCase();
  ///alert (str)
  var pieces = str.split(" ");
  for ( var i = 0; i < pieces.length; i++ )
  {
    var j = pieces[i].charAt(0).toUpperCase();
    
    pieces[i] = j + pieces[i].substr(1);
  }
      
  return pieces.join(" ");
}

/// Callback to get values for form
Method LoadForm(
  pKey As %String,
  ByRef pValues As %String) As %Status
{
  s pValues("Relation") = $g(^tmp,"BLACKFIN CAPITAL PARTNERS")
  q $$$OK
}

/// Callback to process values submitted for form.
ClassMethod SubmitForm(pSubmit As %ZEN.Submit) As %Status
{
  k ^tmp
  s:pSubmit.%Action="save" ^tmp=pSubmit.%GetValue("Relation")
  q $$$OK
}
}

SAMPLES>d $system.SQL.Shell()
SQL Command Line Shell
----------------------------------------------------
 
The command prefix is currently set to: <>.
Enter q to quit, ? for help.
SAMPLES>>?=CALL %SYSTEM.SQL_TableExists('Sample.Person')
1.      ?=CALL %SYSTEM.SQL_TableExists('Sample.Person')
 
 
executing statement with parameter values: set %tResult=%tStatement.%Execute()
 
 
Output Values:
 
 0. 1
statement prepare time(s)/globals/lines/disk: 0.0025s/14/862/0ms
          execute time(s)/globals/lines/disk: 0.0003s/7/179/0ms
                          cached query class: %sqlcq.SAMPLES.cls2
---------------------------------------------------------------------------
SAMPLES>>

Demo for [F1], [F7] and [Home]:

s key(##class(%xsd.hexBinary).XSDToLogical("1B5B31387E"))="F7"
s key(##class(%xsd.hexBinary).XSDToLogical("1B4F50"))="F1"
s key(##class(%xsd.hexBinary).XSDToLogical("1B5B317E"))="Home"
u:$zu(96,14)=1 0:(:"+S") r "Input: ",*x u:$zu(96,14)=1 0:(:"-S")

;zzdump $key
   
w "You press [",$g(key($key),"unknown"),"]",!

Indicates that your version is below 2011.x

See documentation:
2010.2 (absent)
2011.1 (present)

#dim list As %ListOfDataTypes
d ##class(%ZEN.Auxiliary.jsonProvider).%ConvertJSONToObject("[""a"",""b"",""c""]",,.list)
w list.Count(),!

It is not clear what it will give.
To Richard need to save the binary data encoded in hex.

For example, instead of '0x2122232425262728292A2F' to the database should persist the value !"#$%&'()*/

USER>w $c(33,34,35,36,37,38,39,40,41,42,47)
!"#$%&'()*/

USER>w ##class(%xsd.hexBinary).LogicalToXSD($c(33,34,35,36,37,38,39,40,41,42,47))
2122232425262728292A2F

USER>zzdump ##class(%xsd.hexBinary).XSDToLogical("2122232425262728292A2F") ; 0x omitted
 
0000: 21 22 23 24 25 26 27 28 29 2A 2F                        !"#$%&'()*/