I am POSTing in php:
$hwPostData['set_row_field.'.$rownr.'.Spec']='Some product name <>';

....
curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($hwPostData,'','&',PHP_QUERY_RFC3986));

and this results in ORVc.Spec field value in SERP:
Some%20product%20name%20%3C%3E

So I can see the text is not decoded before storing to the SERP DB.

If I send plain text not urlencoded then it is saved as is:
I am sending
set_field.CustCode=100004&set_field.Comment=Some comment&set_field.OrderClass=WEB&set_field.CustOrdNr=WebRest 2&set_field.PlanShip=2020-04-05&set_field.ShipAddr0=ShipAddr0&set_field.ShipAddr1=ShipAddr1&set_field.ShipAddr2=ShipAddr2&set_field.ShipAddr3=ShipAddr3&set_field.Phone=+37061269996&set_row_field.0.ArtCode=10102&set_row_field.0.Quant=2&set_row_field.0.Price=123.45&set_row_field.0.VATCode=PVM1

and this results in Comment field value "Some comment" and CustOrdNr value "WebRest 2" with no spaces converted to plus signs or %20.

I don't use any hal functions, I am just trying to use rest api v.2.2 with basic http auth, because oauth crashes the server (bug is already reported)