How to format Db2 timestamp with UTC consideration

Given the following DB2 Script:

WITH ranked_dataset AS (
    SELECT 
        D.INSTNB AS Id,
        D.INSTNB AS transferId,
        H.FRSTCD AS fromStoreId,
        H.TOSTCD AS toStoreId,
        D.SENDDT AS sendDate,
        D.STANTS AS time_stamp,
        CASE 
            WHEN C.INSTNB IS NOT NULL THEN 'RECIEVED'
            ELSE 'SENT'
        END AS direction,
        json_arrayagg(
            json_object(
                'plu' value D.PRODCD,
                'quantity' value D.TRANQT,
                'sentProcessedTimestamp' value D.STANTS                 
            )
        ) items,
        ROW_NUMBER() OVER (PARTITION BY D.INSTNB, H.DIRECT, H.FRSTCD, H.TOSTCD, D.SENDDT ORDER BY D.STANTS DESC) AS rn
        
    FROM 
        SBOSFILES.HUBISTDT D
    INNER JOIN 
        SBOSFILES.HUBISTHD H
    ON 
        D.INSTNB = H.INSTNB
        AND D.FRSTCD = H.FRSTCD
        AND D.TOSTCD = H.TOSTCD
    LEFT JOIN
        SBOPFILES.HUBISTC C
    ON
        D.INSTNB = C.INSTNB
    WHERE
        H.DIRECT = 'T'
        AND DATE(D.STANTS) = '2018-04-30'
    GROUP BY 
        D.INSTNB,
        H.DIRECT,
        H.FRSTCD,
        H.TOSTCD,
        D.SENDDT,
        D.STANTS,
        C.INSTNB
)
SELECT json_object(
    'id' value (Id || '-' || direction),
    'transferId' value transferId,
    'fromStoreId' value fromStoreId,
    'toStoreId' value toStoreId,
    'sendDate' value sendDate,
    'time_stamp' value time_stamp,
    'direction' value direction,
    'items' value items FORMAT JSON
    )
FROM ranked_dataset  
WHERE rn = 1          
LIMIT 100

Which currently produces an output like this:

{"id":"1-SENT","transferId":1,"fromStoreId":2,"toStoreId":3,"sendDate":"2018-04-30","time_stamp":"2018-04-30-06.55.47.349000","direction":"SENT","items":[{"plu":25,"quantity":10,"sentProcessedTimestamp":"2018-04-30-06.55.47.349000"}]}

I need to make a change so that the parent object 'time_stamp' property and the child objects 'sentProcessedTimestamp' properties would be in this format:

"timestamp": "2018-04-30T05:55:47.349+01:00"

I have tried doing:

TO_CHAR(D.STANTS, 'YYYY-MM-DD"T"HH24:MI:SS.FF3') || '+01:00' AS time_stamp,  

But I get the following error:

An error occurred while processing the results. - Format string not valid for function VARCHAR_FORMAT.. SQLCODE=-20447, SQLSTATE=22007, DRIVER=4.19.56

Further Context

This query will be run from an Azure Data Factory pipeline, and will send to a blob storage container, which an azure function will pick up and insert into mongo db. We expect everything inserted into mongo will be UTC.

Not ideal but this is the best I come up with:

with xx as (
  select CURRENT TIMESTAMP as ats FROM sysibm.sysdummy1
)
SELECT replace(to_char(ats, 'YYYY-MM-DD HH24:MI:SS.FF3'),' ' ,'T')  from xx