Unable to export a transparent GIF "An unknown error has occured"

[E_B_B]

I created a very quick animation in After Effects with a transparent background.
(1920 x 1080 px, Frame Rate 29.97, 4 seconds long)
I exported it in the Render queue using Quicktime (fomat settings video codec animation) and channels RBG + Alpha. 
It exported just fine with the transparent background, however my client can't use MOV file types in their video editing software, so I tried to change it into a Gif in Photoshop CC 2019.

No matter the frame rate or the px size of the file, I always get the same error message when I try to export < save for web (legacy). I'm really not to sure what I'm doing wrong. I've followed advice in this forum and video tutorials online. If anyone knows what I'm doing wrong please let me know, I've been trying to sort this out for days now 😞

[Triny]

Hey! did you solved it? The same is happening to me. Same message, the weirdiest thing is that I'm making a series of animations and I had not problem with the previous ones, and if I get those mov files again, I can use the "Save for Web (Legacy)" and create the animated gif, but not with anything new.

[Triny]

I ended up generating it on Media Encoder successfully.