Multidigit Addition in assembly

Question

I'm trying to use this code for multidigit addition in assembly using user input, but I'm not getting the correct result

SYS_EXIT  equ 1
SYS_READ  equ 3
SYS_WRITE equ 4
STDIN     equ 0
STDOUT    equ 1


segment .data
    msg db "The sum is: "
    len equ $-msg
    
    msg2 db "Input num1: "
    len2 equ $-msg2
    
    msg3 db "Input num2:"
    len3 equ $-msg3
    
    lf db 0x0A

segment .bss
    sum resb 40                 ; 40 Bytes for an ASCII string
    sum_len resd 1
    
    number1 resb 40
    number2 resb 40
    num1_len resd 1
    num2_len resd 1
    

section .text
    global _start

_start:
    
    
    ; Output "input num1"
    mov ecx, msg2
    mov edx, len2
    mov ebx, 1
    mov eax, 4
    int 0x80
    
    ;read ans store input1
    mov eax, SYS_READ 
    mov ebx, STDIN  
    mov ecx, number1 
    mov edx, 3
    int 0x80
    
    lea esi,[number1]
    mov ecx,4
    call string_to_int
    
    ; Output "input num2"
    mov ecx, msg3
    mov edx, len3
    mov ebx, 1
    mov eax, 4
    int 0x80
    
   
    ;read ans store input2
    mov eax, SYS_READ 
    mov ebx, STDIN  
    mov ecx, number2 
    mov edx, 3
    int 0x80
    
    lea esi,[number2]
    mov ecx,4
    call string_to_int

    ; Addition
    mov eax, [number1] 
    mov ebx, [number2]
   
    add eax, ebx


    ; Convert the number to a string
    mov edi, sum                ; Argument: Address of the target string
    call int2str                ; Get the digits of EAX and store it as ASCII
    sub edi, sum      
    mov [sum_len], edi

    ; Output "The sum is: "
    mov ecx, msg
    mov edx, len
    mov ebx, 1
    mov eax, 4
    int 0x80

    ; Output sum
    mov eax, 4
    mov ebx, 1
    mov ecx, sum
    mov edx, [sum_len]
    int 0x80

    ; Output Linefeed
    mov eax, 4
    mov ebx, 1
    mov ecx, lf
    mov edx, 1
    int 0x80

    ; Exit code
    mov eax, 1
    mov ebx, 0
    int 0x80

; Input:
; ESI = pointer to the string to convert
; ECX = number of digits in the string (must be > 0)
; Output:
;EAX = integer value

string_to_int:
   xor ebx,ebx    ; clear ebx
.next_digit:
   movzx eax,byte[esi]
   inc esi
   sub al,'0'    ; convert from ASCII to number
   imul ebx,10
   add ebx,eax   ; ebx = ebx*10 + eax
   loop .next_digit  ; while (--ecx)
   mov eax,ebx
   ret
  
int2str:    ; Converts a positive integer in EAX to a string pointed to by EDI
    xor ecx, ecx
    mov ebx, 10
    .LL1:                   ; First loop: Save the remainders
    xor edx, edx            ; Clear EDX for div
    div ebx                 ; EDX:EAX/EBX -> EAX Remainder EDX
    push dx                 ; Save remainder
    inc ecx                 ; Increment push counter
    test eax, eax           ; Anything left to divide?
    jnz .LL1                ; Yes: loop once more

    .LL2:                   ; Second loop: Retrieve the remainders
    pop dx                  ; In DL is the value
    or dl, '0'              ; To ASCII
    mov [edi], dl           ; Save it to the string
    inc edi                 ; Increment the pointer to the string
    loop .LL2               ; Loop ECX times

    mov byte [edi], 0       ; Termination character
    ret                     ; RET: EDI points to the terminating NULL