Sending UTF-8 extended characters, they appear in the testing panel as question marks (?). It is not clear where that conversion is taking place - at the gateway, or within the Guzzle client.
The gateway test panel is a shameless ISO8859-1, but UTF-8 encoded characters that fit into the extended ASCII set are being correctly converted somewhere. So Iñtërnâtiônàlizætiøn as UTF-8 is displaying as Iñtërnâtiônàlizætiøn in the testing panel. But アイウエオカキクケコサシスセソタチツテ goes over as ???????????????????. The character counts are correct, so something is making a good attempt at converting the UTF encoding, but is using "?" as the out-of-bounds replacement character.
Sending UTF-8 extended characters, they appear in the testing panel as question marks (?). It is not clear where that conversion is taking place - at the gateway, or within the Guzzle client.
The gateway test panel is a shameless ISO8859-1, but UTF-8 encoded characters that fit into the extended ASCII set are being correctly converted somewhere. So
Iñtërnâtiônàlizætiøn
as UTF-8 is displaying asIñtërnâtiônàlizætiøn
in the testing panel. Butアイウエオカキクケコサシスセソタチツテ
goes over as???????????????????
. The character counts are correct, so something is making a good attempt at converting the UTF encoding, but is using "?" as the out-of-bounds replacement character.