Unable to suggest mods, says that it is not valid

Hello, i've been trying to organize myself with a small creative build project resulting in an adventure map. However, one of the mods required for this project is not available on Aternos, and despite multiple attempts, it says that the URL is not valid. The mod is from CurseForge, and it works properly when pasted in, so idk what is the issue.

https://www.curseforge.com/min…mc-mods/super-castlevania

So they're impossible to add because of this issue. Gotcha. Tnx for answering.