How to fix: Invalid conversion from 'const char*' to 'char*' [-fpermissive]
This begin()
method expects a modifiable character array as its first argument. That's what you should provide:
char ssid[] = "YOUR_SSID"; // this is changed
const char* password = "YOUR_PASSWORD"; // this is fine
[...]
WiFi.begin(ssid, password);
The location where you are calling the function begin, has as first parameter a parameter of type const char* instead of char* ... remove the const from this argument type.
Probably you have something like
const char* s = ....
...
...begin(s, ...)
Change class s to
char* s = ...