Beginner issues - STM32F767VI and no action on QSPI pins

First, I am new to STM32, MBED OS, and C++/OO, but as of now I am at least able to write and
compile some meaningful code, and make it run on the STM32.

On my custom STM32 board, the MCU QSPI interface is hooked up to an S2FL064 flash chip.
I have tried to compile the test code found on this site, and while it compiles and runs,
it reports error message in terminal very early in the program (“Write Enable failed”).

I have scoped the QSPI pins, and found no activity at all there. I built a short loop
to repeat reads of QSPI to be sure of this.

In my custom_target.json file, I have the following relevant fields:

    "components_add": [
		"QSPIF"
    ],

	"device_has_add": [
		"QSPI"
	],

In PinNames.h:

// QUAD SPI FLASH
QSPI_FLASH1_IO0 = PE_7, // <->
QSPI_FLASH1_IO1 = PE_8, // <->
QSPI_FLASH1_IO2 = PE_9, // <->
QSPI_FLASH1_IO3 = PE_10, // <->
QSPI_FLASH1_SCK = PB_2, // ->
QSPI_FLASH1_CSN = PC_11, // ->

QSPI1_IO0 = PE_7,                   // <->
QSPI1_IO1 = PE_8,                   // <->
QSPI1_IO2 = PE_9,                   // <->
QSPI1_IO3 = PE_10,                  // <->
QSPI1_SCK = PB_2,                   // ->
QSPI1_CSN = PC_11,                  // ->           

The pin layput for the STM32 board was layed out in the STM32CubeMX software.
Due to other pin arrangements, the QuadSPI pin definition selected here is “Bank2 with QUAD SPI Lines” (as opposed to Bank1).
Do I need to change something lower level to accomodate for this, or is it already taken care of?

main.cpp object creation:

QSPI qspi_device(QSPI_FLASH1_IO0, QSPI_FLASH1_IO1, QSPI_FLASH1_IO2, QSPI_FLASH1_IO3, QSPI_FLASH1_SCK, QSPI_FLASH1_CSN); // io0, io1, io2, io3, sclk, ssel

device configuration:

qspi_device.configure_format(QSPI_CFG_BUS_QUAD, QSPI_CFG_BUS_QUAD, QSPI_CFG_ADDR_SIZE_24, QSPI_CFG_BUS_QUAD, QSPI_CFG_ALT_SIZE_8, QSPI_CFG_BUS_QUAD, 0);

test loop:

    while(true) {
    char status_value[STATUS_REG_SIZE] = {0xFF};
    qspi_device.command_transfer(CMD_RDSR, -1, NULL, 0, status_value, STATUS_REG_SIZE);
    printf("Next read...\r\n");
};

The test loop runs (repeated text can be seen in terminal), but does not cause any activity on the QSPI bus.

I compile code using MBED CLI 1.8.3 and GCC_ARM (latest version) toolchain, and I use Visual Studio Code as editor.
According information in mbed_version.h under \mbed-os\platform\include\platform I am using V6.3 of MBED OS.

Any suggestions are highly appreciated.