How can ESL establish periodic sync with the special AP?

Question

Hi,my board is nRF52840,and the demo is periodic_sync_conn within ncs2.7.0, 
 I want to establish periodic sync with the AP whose rssi is better，but i am failed。Thanks.

struct _AP_info 
 { 
 int8_t sid ; 
 int8_t rssi ; 
 bt_addr_le_t addr ; 
 } __packed ; 
 static struct _AP_info AP_info = {. rssi =- 80 }; 
 
 static void scan_AP ( const struct bt_le_scan_recv_info * info ) 
 { 
 if ( info -> rssi > AP_info . rssi ) 
 { 
 AP_info . sid = info -> sid ; 
 AP_info . rssi = info -> rssi ; 
 bt_addr_le_copy ( & ( AP_info . addr ), info -> addr ); 
 printk ( "Get better rssi AP:sid= %d ,rssi= %i ,addr=0x %X 
 " , AP_info . sid , AP_info . rssi , AP_info . addr . a . val [ 0 ]); 
 } 
 } 
 static void scan_recv ( const struct bt_le_scan_recv_info * info , struct net_buf_simple * buf ) 
 { 
 char name [ NAME_LEN ] = { 0 }; 
 char le_addr [ BT_ADDR_LE_STR_LEN ]; 
 struct _AP_info * p_AP_info = NULL ; 
 
 ( void ) memset ( name , 0 , sizeof ( name )); 
 bt_data_parse ( buf , data_cb , name ); 
 bt_addr_le_to_str ( info -> addr , le_addr , sizeof ( le_addr ));

if ( 0 == strstr ( name , "PAwR conn sample" ) || 0 == info -> interval ){ 
 return ; 
 } 
 
 //printk("scan_recv:%s,sid:%d,rssi:%i,type:%d,addr:%s
", name, info->sid, info->rssi, info->addr->type, le_addr); 
 scan_AP ( info );

if ( ! per_adv_found ){ 
 
 // per_sid = info->sid; 
 // bt_addr_le_copy(&per_addr, info->addr); 
 
 per_sid = AP_info . sid ; 
 bt_addr_le_copy ( & per_addr , & ( AP_info . addr )); 
 
 per_adv_found = true ; 
 k_sem_give ( & sem_per_adv ); 
 } 
 }

static struct bt_le_scan_cb scan_callbacks = { 
 . recv = scan_recv , 
 };