I can not reproduce this, but I only have access to

✔ 19:41:06 $ python --version
Python 3.7.10 (51efa818fd9b24f625078c65e8e2f6a5ac24d572, Apr 11 2021, 13:25:22)
[PyPy 7.3.4 with GCC 10.2.0]

which pulls matplotlib-3.3.4-pp37-pypy37_pp73-manylinux2010_x86_64.whl

attn @mattip .

That C-API function was added in PyPy v.7.3.2. Please update to the latest PyPy version.

Lets close for now, but @yuan8901 please ping us if that doesn't fix the problem.

If the pypy wheels can't specify micro-release version requirements, perhaps the version check at the point of use

#if defined(PYPY_VERSION) && (PYPY_VERSION_NUM  < 0x07030200)
        Py_UNICODE *unistr = PyUnicode_AsUnicode(textobj);
        for (size_t i = 0; i < size; ++i) {
            codepoints[i] = unistr[i];
        }
#else
        for (size_t i = 0; i < size; ++i) {
            codepoints[i] = PyUnicode_ReadChar(textobj, i);
        }
#endif

should just use a version bound of 0x07040000? This way the wheels stay always valid, even though they may use a slightly less optimal version on PyPy 7.3.{0,1}.