Please correct my function ?

char *SIM_TxBuffer;

sizeof(aTxBuffer))

strings are null terminated, use it to calc the length.

Compiler will not simply even if main is in the same code file as the function...

I don't know how do you manage aTxBuffer, but I suspect that may be another point of failure.

First, Array is not pointer, pointer is not array

char* a = "Test string", int* b;
sizeof(a) // is 4
sizeof(b) // is also 4
//sizeof gives you size of the pointer, not the data it points to
char c[] = "Test string";
sizeof(c) // is 12, it is the same as sizeof(char[12]), which is size of the array itself
strlen(a) //is 12 too, this is a function that counts the length of a string

You can simply replace sizeof(SIM_TxBuffer) with strlen(SIM_TxBuffer) for simpler code, but I prefer passing length as a parameter for better optimization on constant length commands.

void sim7600_modem(char *SIM_TxBuffer, size_t length)
{
 printf("sim7600_modem ATI\r\n");
 //Clear buffer
 HAL_UART_Transmit_IT(&huart1,(uint8_t*)&aTxBuffer4, sizeof(aTxBuffer4));
 HAL_Delay(5);
 HAL_UART_Transmit_IT(&huart1,(uint8_t*)SIM_TxBuffer, length);
 
 HAL_UART_Receive_IT(&huart1, (uint8_t *)&SIM900.rxBuffer,1);
} 
 
const char command[] = "ATI\r";
sim7600_modem(command, sizeof(command));