When creating a ZPL International Label with suppressPostage = true, like:
"imageInfo": {
"imageType": "ZPL203DPI",
"labelType": "4X6LABEL",
"receiptOption": "NONE",
"suppressPostage": true
},
The postage is no longer suppressed but is printed on the label. I have not tested label types other than ZPL203DPI. The postage used to be correctly suppressed but this stopped working at some point this fall I believe.