I can't fix this encoding error, how can I solve it?

Question

PHP

SOAP-ERROR: Encoding: string '\x94...' is not a valid utf-8 string
In short, as far as I understand, the text that is sent via SOAP must be in valid utf-8 encoding. The text itself consists only of Latin letters. Script in yutf-8 encoding. I tried to pass the text through the functions: utf8_encode('zzzz'), mb_convert_encoding('zzzz', "utf-8", "auto"); did not help!

Answer 1

A text consisting only of Latin letters is already a valid utf8 text; it does not need to be encoded additionally
\x94 - this is not Latin, these are additional codes from the higher digits of ASCII and related one-byte encodings, usually there were Cyrillic, diacritics, pseudographics and so on.