WebApi action Consumes/Produces XML must accept non utf8 encoding

[vhforte]

Hi All,
I am using net6 webApi project. Controller action is supposed to consume/produce XML and has these attributes:

[Consumes("application/xml")]
[Produces("application/xml")]

in the starup file I added this:
services.AddControllers(...).AddXmlSerializerFormatters()

It works well as long as incoming request has utf-8 encoding i.e.
new StringContent(xmlText, Encoding.UTF8, "application/xml");

But I want to send request using Encoding.GetEncoding("iso-8859-1").
The header in XML document is changed accordingly.
When I use iso-8859-1 - the call fails, before the controller action with response 415 - Unsupported Media Type.
What can I do to make the controller action accept iso-8859-1 ?
Thank you.