Cannot use field repair tools

[Scared]

I have 2 field repair tools and a master repair tool, but i can't use either one in Mushin's tower, Nightshade harbor or e fleet harbor.

My weapon's durability is usually at around 10/100 when i try it. Does my weapon have to be broken to use it or is there just something wrong for me?

Are they not meant to be used in these places?

[Emya]

I think you need 3 field repair tools to be able to do repairs.

As for the master repair tool, I don't know since I haven't had a chance to use it.