Can't call between 2 SPA3000

I have setup FreePBX with 4 Softphone, and 2 SPA3000.
extension setup:
SPA3000 - ext 101 (internal network)
SPA3000 - ext 102 (connect over internet)
Softphone - ext 103 (connect over internet)
Softphone - ext 999 (internal network)
Softphone - ext 998 (internal network)

from 101, I can call all other extension except 102 (resp 486 busy here), calling *43 works fine.

from 102, I can call all extension, but calling to 101 no audio.
calling to *43 is works fine thou.

from any softphone I can call any extension and working fine.

I have no clue where is the problem when i’m trying make call between the spa3000

*note both spa3000 are having the same firmware (3.1.20)