std::thread(&foo::bar ..) throws an error after converting bar from static to non-static method [duplicate]

I have class foo. The bar method used to be static and I was able to create new threads with the code below. I

class foo
{
public:
    static void bar(std::unique_ptr<std::vector<std::string>> pData)
    {
        // do things here
    }
};

auto pDdata = std::unique_ptr<std::vector<std::string>>(new std::vector<std::string>);
std::thread newThread = std::thread(&foo::bar, std::move(pData));

Then I changed the bar method a little. Notice that due to the size_data declaration, bar is no longer static.

    void bar(std::unique_ptr<std::vector<std::string>> pData)
    {
        unsigned short int size_data = pData.get()->size();
        // do things here
    }

At this point, the compiler started giving an error.

/usr/include/c++/7/thread:240:2: error: no matching function for call to ‘std::thread::_Invoker<std::tuple<void ...

Then, I tried changing

std::thread newThread = std::thread(foo::bar, ...)

and I started receiving the following error.

error: invalid use of non-static member function

I'm not sure what's wrong. Any help is appreciated.