Do you unlock the another fusion slot or for only on time

You know the one where if one of your creatures is getting fused and want to fuse another Dino and need to pay bucks for it is it unlock or one time

One time.

Oh well I was hoping for an unlock

It s not bad anyway.
I d like to use the unlock slot for those dino that use much time to evolve or fuse eg, indo rex lv 10-11, 20-21, Tournament creatures at high level, hybrid creatures(super rare, legend).
If the first slot if empty, i ll put triceratops in it first.