When you open the "Upload Body" text editor, you can double click in the attributes on the left side to insert them.

Unfortunately, I cannot get results. I am trying to upload 4 columns of data with +100 rows. When I do as you suggest, I manage to upload one row only. Do you have any advise on the text edition?

Thanks a million Niels!

If you have 100 features with 4 attributes (imo,mmsi,ship_name,call_sign) use StringConcatenator or

AttributeManager or AttributeCreator to concatenate them in a single attribute then in an Aggregator select the concatenated attribute in Attributes to Concatenate (and set the necessary Separator Character - ENTER/LF).

The result will be your Upload Body string. Or at least part of it.

You can also type in your Content Type as text/csv instead of setting it via Header

Thank you all! I am still fine tuning to get the desired results, but your answers unblocked my workspace.