http client multipart form data 400 (Bad Request) response

I apologize in advance for the long post.  I'm struggling with multipart forms and continue to get response 400 (bad request).  The specifications are as follows:

/*  requirements */

A file can be added to the request by the "operations" relation (the "uri" field for the "rel = operations" object in the above example). The POST to this URL requires the request content type "multipart/form-data". This URL can be invoked multiple times to send multiple files in one request. The request body must contain fields named:

blob: the file, converted to an array of bytes

checksum: a checksum generated by you so that POS can validate receiving the correct data

algorithm: the algorithm used to generate the checkum. Polling will reject the request unless using one of SHA-1, SHA-256, SHA-384, and SHA-512

transforms: a comma-separated list of any packaging or compression applied to the file (zip, bzip, tar, etc.), listed in the order POS should execute to un-package the file

/*  end requirements */

There's obviously something wrong with my code below but I can't figure it out.  I'm sure it's my ignorance but hopefully, someone can help cure that.

Thanks in advance,

// File

ASSIGN 
    oMultiEntity          = NEW MultipartEntity()
    oMultiEntity:Boundary = GUID .
CREATE X-DOCUMENT hSoapDocument.
hSoapDocument:LOAD('file':u, fileSubmission, FALSE /* validate */ ).
hSoapDocument:SAVE('memptr':u, mData).
     
     
ASSIGN 
    oSoapDoc        = NEW MEMPTR(mData)
    oPart           = NEW MessagePart('application/octet-stream':u, oSoapDoc)
    oPart:ContentId = 'blob':u.
           
oMultiEntity:AddPart(oPart).
    
// Hash
set-size(mData) = 0.
 
DEFINE VAR r AS RAW NO-UNDO.

// Not sure if this is the correct approach???
r = MESSAGE-DIGEST("SHA-256",lcFileSubmission).
   
SET-SIZE(mData) = LENGTH(r).
mData = r. 

ASSIGN 
    oHash           = NEW MEMPTR(mData)
    oPart           = NEW MessagePart('text/plain':u, oHash)
    oPart:ContentId = 'hash':u
    .
oMultiEntity:AddPart(oPart).

//algorithm   = "SHA-256".
set-size(mData) = 0.

DEF VAR algorithm AS LONGCHAR NO-UNDO INIT "SHA-256". 
SET-SIZE(mData) = LENGTH("SHA-256") + 1.
PUT-STRING(mData,1) = "SHA-256". 
   
ASSIGN 
    oAlgorithm      = NEW MEMPTR(mData)
    oPart           = NEW MessagePart('text/plain':u, oAlgorithm)
    oPart:ContentId = 'algorithm':u
    .
oMultiEntity:AddPart(oPart).

//transforms
set-size(mData) = 0.

DEF VAR transforms AS LONGCHAR NO-UNDO INIT "". 
SET-SIZE(mData) = LENGTH(transforms) + 1.
PUT-STRING(mData,1) = transforms. 
   
    

ASSIGN 
    otransforms     = NEW MEMPTR(mData)
    oPart           = NEW MessagePart('text/plain':u, otransforms)
    oPart:ContentId = 'transforms':u
    .
oMultiEntity:AddPart(oPart).


 
 
httpClient  = ClientBuilder:Build():Client.
oCreds = NEW Credentials('smisdev.mydomain.com', 'abc', 'abc123').

FIND FIRST links WHERE links.rel = "operations" NO-LOCK NO-ERROR.
oRequest = RequestBuilder:Post(links.uri, oMultiEntity)
:UsingBasicAuthentication(oCreds)
:ContentType('multipart/form-data')
:AcceptJson()
:REQUEST.
 

oResponse = httpClient:Execute(oRequest).
MESSAGE oResponse:StatusCode SKIP oResponse:StatusReason VIEW-AS ALERT-BOX.