Seems to be a bug when you sometimes earn a new incantation. The same happened to me when I killed the plague dragon but restarting seemed to fix it.

your faith stat is too low

your faith stat is too low to access it

Reload your game I had the same issue

The altar only works at night

Same for me, it fixed itself after i rested at the site of grace a bit to the left of it.

Rest at a grace and return, it's touchy.

if you are having the same issue just go to main menu and load back in. It will work

Resting at a site of grace fixes it, same thing happened to me

Only works at noon, so pass time in the bonfire menu.

Travel to the site of grace then try

It's not time dependant you dinguses, you just have to reload by either quit-out or grace rest

It works for me by just doing it on the side, and not in front

You need a sacred seal to use them, which is a type of weapon. The one for boosting damage with dragon incantations is the dragon communion seal which is in the first stone sword door in the starting dungeon.

you need to use and incantation

You need to use the finger seal for incantation

No one asked for your "hint" (spoiler) dumbass.

The spell or the dragon hearts?

Good to know..thank you. Ignore the idiot complaining about spoilers on a wiki post with a list of end game area dragons lmfao.