Webhook for Deleting Multiple Attachment File

Hi All, 

I am new for the Webhook / API. I would like to create a webhook to delete attachment for a portion of the records. A new field called "Webhook Trigger" is created (containing 0 or 1), to determine which records should trigger the webhook. 

By referencing this discission (Automatically Delete File Attachments Upon Data Change), I have created below Webhook for modified records with "Webhook Trigger" = 1.

HTTP method: POST

Message format: XML

Message header: QUICKBASE-ACTION          API_EditRecord

<qdbapi>
<usertoken>xxxSAMPLE_USERTOKENxxx</usertoken>
<rid>[Record ID#]</rid>
<field fid="189" filename="delete"></field>
</qdbapi>

However, it only works for the first record, and no effect for the rest of the records. Is there any other way so that multiple record deletion of attachment can be performed? Thanks so much!