Trouble writing option byte in STM32G030

[EKoec]

I'm trying to write the option byte in my STM32G030 uC to be able to start the internal boot loader by pulling BOOT0 high (set nBOOT0_SEL = 0). The problem is I'm getting a WRPERR while writing. All other related registers are in default state. If I use HAL_FLASH_Program(..) instead, I get the same error at the same step. Any ideas?

const uint64_t u64_option_byte_boot = 0x00000000DEFFE1AA;
 
HAL_FLASH_Unlock();
HAL_FLASH_OB_Unlock();
 
FLASH_WaitForLastOperation(FLASH_TIMEOUT_VALUE);
 
// set PG
FLASH->CR |= 0x01;
 
*p_u32_option_bytes = (uint32_t) (u64_option_byte_boot); // <<< after this step FLASH->SR.CFGBSY is set
*(p_u32_option_bytes + 1U) = (uint32_t) (u64_option_byte_boot >> 32); // <<< after this step FLASH->SR.WRPERR is set 
 
FLASH_WaitForLastOperation(FLASH_TIMEOUT_VALUE);
 
SET_BIT(FLASH->CR, FLASH_CR_OPTSTRT);
 
HAL_FLASH_OB_Lock();
HAL_FLASH_Lock();

[TDK]

Use HAL_FLASHEx_OBProgram to manage option bytes, or duplicate its functionality.

Check and clear flash error flags prior to first access. Sometimes they are set.

[EKoec]

Okay, thanks for the hint. This is not very good documented. The solution seems to be:

 FLASH_OBProgramInitTypeDef user_bytes;
 
 HAL_FLASHEx_OBGetConfig(&user_bytes);
 
 user_bytes.USERConfig &= ~(0x1 << 24);
 
 HAL_FLASH_Unlock();
 HAL_FLASH_OB_Unlock();
 HAL_FLASHEx_OBProgram(&user_bytes);
 HAL_FLASH_OB_Launch();
 HAL_FLASH_OB_Lock();
 HAL_FLASH_Lock();

Thanks again.