member access within misaligned address 0x000000000002 for type 'struct ListNode', which requires 8 byte alignment - while-loop

Question

How can I solve this misaligned address problem.I came across this problem when I try to solve addition of two numbers using linked list in reverse order in LeetCode
ProblemLink:https://leetcode.com/problems/add-two-numbers/
algorithm : Ive created a variable flag to check for carry over.When i tried to add the first element of linked list 1 with the first element of linked list 2 ,its throwing an error.
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* struct ListNode *next;
* };
*/
struct ListNode* addTwoNumbers(struct ListNode* l1, struct ListNode* l2){
struct node{
int num;
struct node *ptr;
};
struct node* create(){
struct node *ptr1=malloc(sizeof(struct node));
ptr1->ptr=NULL;
return ptr1;
}
struct node *head=NULL;
struct node *temp=NULL;
int flag=0;
while(l1!=NULL && l2!=NULL){
if(head==NULL){
head=create();
temp=head;
}
else{
temp->ptr=create();
temp=temp->ptr;
}
int a=(l1->val); //showing error
a=a+(l2->val);
a=a+flag;
int b=a%10;
flag=(a-b)/10;
temp->num=b;
l1=l1->val;
l2=l2->val;
}
while(l1==NULL && l2!=NULL){
if(head==NULL){
head=create();
temp=head;
}
else{
temp->ptr=create();
temp=temp->ptr;
}
int a=(l2->val)+flag ;
int b=a%10;
flag=(a-b)/10;
temp->num=b;
l2=l2->val;
}
while(l1!=NULL && l2==NULL){
if(head==NULL){
head=create();
temp=head;
}
else{
temp->ptr=create();
temp=temp->ptr;
}
int a=(l1->val)+flag ;
int b=a%10;
flag=(a-b)/10;
temp->num=b;
l1=l1->val;
}
while(l1==NULL && l2==NULL && flag==1){
if(head==NULL){
head=create();
temp=head;
}
else{
temp->ptr=create();
temp=temp->ptr;
}
temp->num=1;
flag=0;
}
return head;
}