Python ctypes parameter with DLL - pointer to array of doubles

I'm a novice programmer using ctypes with Python and trying to use functions from a DLL written in C. I've found a lot of similar questions on SO to solve, but none of the answers to this kind of conundrum.

I have the DLL loaded just fine, but one of the functions I need to call requires a pointer to an array of 6 doubles to dump the values ​​into, but I can't figure out how to provide what that function needs via Python . (My failed attempt to do this in C is another story.)

I've tried various permutations of ctypes.POINTER(c_double), using byref(), POINTER(c_double*6), etc, and for all of them I get either a type error, or preferably an access violation.

From the DLL documentation:

int swe_calc_ut (double tjd_ut, int ipl, int iflag, double* xx, char* serr)

The function calculates using the time in Julian day to return the planetary body's longitude, latitude, etc. as double.

The closest I've come to passing the data type the DLL will accept is with this code, just trying to get any of the 6 doubles from swe_calc_ut:

dll = windll.LoadLibrary(# file path)

# retype the args for swe_calc_ut
py_swe_calc_ut = dll.swe_calc_ut
py_swe_calc_ut.argtypes = [c_double, c_int, c_int, c_double, c_char_p]
py_swe_calc_ut.restype = None

tjd = c_double(# some value from elsewhere)

returnarray = c_double()
errorstring = create_string_buffer(126)

py_swe_calc_ut(tjd, c_int(0), c_int(64*1024), returnarray, errorstring)

When I try to run as is, I get the error:

OSError: exception: access violation writing 0x0000000000000000

Using byref() gives me a type error, etc.

I'd be forever grateful if someone could point me in the right direction to get the doubles I need from the original DLL function; I'm so frustrated I can't figure this out.