Why can't you interact with some affix when you craft ?

[StyliShShowtime]

When I try to forge items, sometimes I can do something with affixes, but sometimes I can't, I don't seem to understand what let me modify them. Could anymone enlighten me ?

[Nigerian Prince]

The item may have no forging potential left, you don't have any shards for the available affix slots, or you aren't high enough level to forge anymore on that item.

[Astasia]

An item can only have 2 prefixes and 2 suffixes, each affix is only one of those things, health is always a suffix and can not be added as a prefix. If it already has 2 of one of those then you will not be able to add any more affixes of that type.

[StyliShShowtime]

Well, the item has 29 forge potential left, I have 30 shards of this type... How do I know which level I must be to forge more of an item ?

[Astasia]

It tells you at the bottom of the craft screen if you are too low level to increase an affix.

[symphony]

affixes also max at level 5 (in crafting bench)

[Fanger]

Reinforcing the difference on prefixes and suffixes. You can’t use them interchangeably