So I am first time DM'ing a campaign and all of my players have selected manual HP to roll the additional HP they get on each level up. For all but one person, DND beyond automatically changed their HP on the lvl up instead of us rolling. Is this a bug or are we doing something wrong. I mean we know how to correct it by going into the manage hp and manual entering the roll in the rolled HP but for the newbies that dont remember everything its annoying if they cant remember what it was and DND beyond changed it for them.

Lets say a characters hit die is 1d8... so on Lvl 2 they would roll a 1d8, add their constitution modifier and then add that total to their max HP they had before?

Thanks for the help!

That player must have set their HP to “average” instead of “manual,” that’s the only way the character sheet would do it automatically. And you don’t need to add the Constitution modifier at every level-up, the character sheet does that automatically too, you just need to enter the correct number rolled on the die itself.