Ipsec VPN created between XG and SG. but cannot ping

I am new here and need help figuring out this problem. 

I have created a site- to -site connection. 

Site A IP-> 10.0.0.1/24 

Site B IP -> 10.0.2.1/24

While on either internal network I can ping across to any device.

When I VPN into site B from an external network I can ping devices on Site A 

But when I VPN into  Site A from an external network I cannot ping anything on Site B

I have read every article, and every possible solution found on the internet but nothing has worked so far. 

Please help?????