Duplicate key error on custom table with autopk="true"

[A_B_SE]

Hi,

We are experiencing a recurring duplicate key error when inserting records into a custom Adobe Campaign Classic schema via a SOAP web service. The error is:
Cannot insert duplicate key row in object 'neolane.LfTmResponseAPIData'
with unique index 'LfTmResponseAPIData_id'

In the schema we have just this:
 <element autopk="true" desc="this schema contains the data as received for TM response data into lf:tmResponseService.jssp"
label="tmResponseAPIData" name="tmResponseAPIData">

What is the correct and supported way in Adobe Campaign Classic to ensure unique IDs and avoid duplicate key errors in this situation?

Do I need to define a an unique key in the schema as below?
<key name="tmResponseIdx">
<keyfield xpath="@field1"/>
<keyfield xpath="@field2"/>
</key>

Or do I need to create a new sequence in xtkNewId? How do I proceed in this case?

Thanks