Cannot Upload City Texture pack, thats been applied for 3 years.

Hello! So I have had a realm open for years with the city texture pack applied. We have built this city based on the city pack. But now since the update, I cannot apply any texture pack to realm, except for the base minecraft texture pack. I have tried to delete the city pack, and redownload it, but everytime I try to apply it to the realm, it says ERROR: some the selected content could not be applied. Please help, as it is really hard to build a world based on the city pack, and have to revert back to the original vanilla minecraft.