When creating shipping labels, the following error occurs:
Shipping labels could not be created: SOAP-ERROR: Encoding: string ... is not a valid utf-8 string
The API user or password contain invalid characters.
The API user and/or password must be changed so they do NOT contain the following characters:
- umlauts (ä, ö, ü)
- ampersand (&)
- German Eszett (ß)
- characters with diacritical marks (for example é, ê, í)
Also note this article about the login configuration.