As Luke pointed out , the brackets are mandatory.

If it does not parse with brackets it is 99.99% due to the fact that you passed a non-null terminated wchar_t string.

The documentation mentions the provided string to be null terminated
A pointer to the NULL-terminated network string to parse.

https://learn.microsoft.com/en-us/windows/win32/api/iphlpapi/nf-iphlpapi-parsenetworkstring