I can only give some prizes if the player has it on their wish list

I receive presents from players who send me things I have in my collections. When I want to give presents like this, they don't show up as possible givewaways. How does that work? I have multiples of things in some collections, that I could share, but if the player doesn't have them on his wish list, I can't seem to give them away....Any solutions for that?

What you can "gift" others depends on your game level and what locations/scenes you have open and what level the scene is.  The program has controlled each item in this manner.  When you look in your collections tab, you will see a collection item (list of five in a collection) and they usually have a "+" sign on them.  Those are collections you can gift to friends.  If there is no sign, then you cannot gift it nor receive it via gift.  Combining items are the four items and their quantity that you must have in order to combine the collection.  So you need all five collection items and the quantities of all four combiner items.  This gives you the collection in your inventory.  Combiner items are "free" to give and show up in your inventory tab while giftable collection items (with the "+" sign) will come out of your inventory, thus not free and are found in the collections tab of the friends you open to gift.

Normally, you can give a collection to anyone that has the ability to receive that item based on the restrictions in my first sentence.  If you open their WL you will see numbers associated with the items.  A blank number means you don't have any to give.  A number one means you can gift it (and if it is a collection item, you will be left with 0).  If the number is 2 or more, these are all collection items and gifting them reduces your inventory by 1.

So from what you say, I believe you either are not at the correct level of some sort to gift the item or there is a problem such as the game is telling you the friend has not played in a while.