Write protection on STM32F779ii - c

Question

I'm trying to erase flash for STM32F779II.
The start up file starts with that section:
{
FLASH (rx) : ORIGIN = 0x08000000, LENGTH = 1664K
DTCMRAM (xrw) : ORIGIN = 0x20000000, LENGTH = 128K
SRAM1 (xrw) : ORIGIN = 0x20020000, LENGTH = 368K
SRAM2 (xrw) : ORIGIN = 0x2007C000, LENGTH = 16K
MEMORY_B1 (rx) : ORIGIN = 0x60000000, LENGTH = 0K
}
So I'm leaving that three sections.
I'm trying to clear sector number 22. but I get Write Protection Error.
Here is how I'm earsing it.
Sectors is an array with one element, which is 22 sector number which has address
0x081C0000
secbool flash_erase_sectors(const uint8_t *sectors, int len,
void (*progress)(int pos, int len)) {
ensure(flash_unlock_write(), NULL);
HAL_FLASH_OB_Unlock();
FLASH_EraseInitTypeDef EraseInitStruct;
EraseInitStruct.TypeErase = FLASH_TYPEERASE_SECTORS;
EraseInitStruct.VoltageRange = FLASH_VOLTAGE_RANGE_3;
EraseInitStruct.NbSectors = 1;
if (progress) {
progress(0, len);
}
for (int i = 0; i < len; i++) {
EraseInitStruct.Sector = sectors[i];
uint32_t SectorError;
if (HAL_FLASHEx_Erase(&EraseInitStruct, &SectorError) != HAL_OK) {
ensure(flash_lock_write(), NULL);
return secfalse;
}
// check whether the sector was really deleted (contains only 0xFF)
const uint32_t addr_start = FLASH_SECTOR_TABLE[sectors[i]],
addr_end = FLASH_SECTOR_TABLE[sectors[i] + 1];
for (uint32_t addr = addr_start; addr < addr_end; addr += 4) {
if (*((const uint32_t *)addr) != 0xFFFFFFFF) {
ensure(flash_lock_write(), NULL);
return secfalse;
}
}
if (progress) {
progress(i + 1, len);
}
}
ensure(flash_lock_write(), NULL);
return sectrue;
}