Charset change in Content Type fails

[phpengine]

Hi guys, I'm implementing testing on a WAF for a client. One of the required tests includes setting a 'Content-Type': 'application/json; charset=UTF-8' . This fails with the below errors. Any ideas for how I can run this please?@

input = <read-only buffer ptr 0x2831b74, size 586 at 0x7fc15e32e170>, errors = 'strict'

    def decode(input, errors='strict'):
>       return codecs.utf_8_decode(input, errors, True)
E       UnicodeDecodeError: 'utf8' codec can't decode byte 0xc0 in position 0: invalid start byte

/usr/lib64/python2.7/encodings/utf_8.py:16: UnicodeDecodeError