Faction Contract not possible to fullfill


I have accepted a Faction contract which says deliver 29 units magnesite to Ant I-Phobos(ZV-307d).
That is where my base is build.
I have the 29 magnesite in base storage, but the fullfill button in the contract is not available!
Why ?

It seems you mixed up magnetite and magnesite. Did you buy it from the commodity exchange?