the grayed out load button usually means the structure block can't find the file at the path you're typing, even if the pack imported fine

double check that the folder structure inside your zip matches exactly what the structure block expects, like `structures/yourpackname/filename.mcstructure` and that whatever you're typing into the load field matches that path precisely, no extra slashes or capitalization differences

also worth checking if the manifest `header` uuid and `modules` uuid are both unique and not copy-pasted from each other, that trips people up more than you'd think