There is a specific character that shows up wrong when UTF-8 is set from the client(SoapUI) in the header content-type: application/json;charset=UTF-8. The character ß shows up as �. If the client does not set the content-type header, the character ß shows up correctly.
SoapUI defaults to iso8859-1 encoding of characters, so setting charset=UTF-8 in the Content-Type header is incorrect for the encoding being used. Postman defaults to using UTF-8 encodiing, so tests with charset=UTF-8 in the Content-Type header work correctly.
The character encoding used in the client and the Content-Type header must be set appropriately for characters from the extended character set to be processed correctly by the gateway
It is possible to override the default encoding used when using SoapUI as the client. We were not able to determine a way to override the default encoding used by Postman, so it will always use UTF-8.