I need to add an attachment while creating a B2B message please help me in creating a valid payload

I need help with creating a B2B message with an attachment using the REST API.

I am calling:POST /fscmRestApi/scm/redwood/11.13.18.05/b2bMessageswith the following payload structure:

<n1:B2BInvoiceMessage xmlns:n1="http://xmlns.oracle.com/apps/scm/cmk/b2b">   
<n1:B2BInvoice>      
<n1:InvoiceNumber>TEST15May02</n1:InvoiceNumber>      
<n1:InvoiceDate>2026-05-15</n1:InvoiceDate>      
<n1:TypeCode>STANDARD</n1:TypeCode>      
<n1:Description>111316939111911111</n1:Description>      
<n1:CurrencyCode>EUR</n1:CurrencyCode>      
<n1:TotalAmount>7.49</n1:TotalAmount>      
<n1:GroupId>20Mar_10-050220261202</n1:GroupId>      
<n1:ExchangeRateType>Corporate</n1:ExchangeRateType>      
<n1:ImportDocumentNumber>1</n1:ImportDocumentNumber>      
<n1:InvoiceReceivedDate>2026-05-15</n1:InvoiceReceivedDate>      
<n1:OperatingUnit>Office Principal BU</n1:OperatingUnit>     
 <n1:Lines>        
 <n1:LineExtensionAmount>7.49</n1:LineExtensionAmount>        
 <n1:OrderNumber>DS100848345</n1:OrderNumber>         
<n1:OrderLineNumber>1</n1:OrderLineNumber>      
</n1:Lines>   
</n1:B2BInvoice>   
<n1:Attachments>      
<n1:FileName>TEST15May01.pdf</n1:FileName>      
<n1:EmbeddedDataBinaryObject>[Base64 PDF content]</n1:EmbeddedDataBinaryObject>   
</n1:Attachments></n1:B2BInvoiceMessage>