A paladin in my game is using great weapon fighting with a greatsword. Per the feature on a roll of 1 or 2 the die is supposed to be changed to a 3, however this does not happen when rolling.  Another issue is with the feat great weapon mastery the additional 2 damage is not automatically added to the heavy weapon rolls as stated in the feat. 

Quote from Mordrax_Allontak >>

A paladin in my game is using great weapon fighting with a greatsword. Per the feature on a roll of 1 or 2 the die is supposed to be changed to a 3, however this does not happen when rolling.  Another issue is with the feat great weapon mastery the additional 2 damage is not automatically added to the heavy weapon rolls as stated in the feat. 

D&D Beyond has never implemented support for either of these in the online dice roller. It doesn't like something they're likely to do anytime soon, unfortunately.

That's beyond what the current dice roller can do. While possible to implement it is low priority and very unlikely to be implemented soon, if ever.

I made a video showing how you can sorta get around this. Hope it helps.