How to import row in CPQ through REST API specifying custom fields

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Hello,

We need to insert some rows in the quotation specifying also some custom fields in a quotation.

However, through the use of the REST API "Create Transaction with Line Items" we can only spcify part number and quantity (with price book if necessary), as written in the note here:

 If we want to insert n rows together specifying also other attributes through REST API, is there a REST API we can use or have we have to use the "Create Transaction with Line Items" or "Create Transaction Lines" first to create the row and then use the "Clean Save" on a single row to save the data (so invoking the service one time for each row)?