UPS API - What encoding should I use?

I'm implementing shipping into my application and I have problems with polish chars. On generated label they appear as '?'. Client is written in C# so al开发者_如何学Gol my strings are Unicode. Maybe you know in what encoding I should send data to get polish chars?

I send:

gęśla jaźń

And on the .gif label there is:

g??la ja??

It seems that UPS expected text in different encoding, but I can't find which.

The code:

 ShipToType upsShipTo = new ShipToType();
 upsShipTo.Name = shipToNameTextBox.Text;

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I've got answer from UPS: api uses latin1 charset so it doesn't support polish chars.