Hi Vina,
The options that are available in the Custom Item Specifics section on the listing composer are actually imported from eBay, so we do not have the ability to choose what options are displayed in those sections.
I'm not sure specifically which category you are listing in but I pulled up category # 63866 (Clothing, Shoes & Accessories > Women's Clothing > Sweaters) and I see that the "Other" option is NOT provided as an option for the attribute called "Size", so I'm assuming that is what you are referring to.
However, I then loaded the same category into the "Sell your Item" form directly on the eBay website and found that the "Other" option is not available for "Size" there either, so it appears that this issue is just a product of eBay not supporting the "Other" option for the attribute called "Size".
One thing that you may be able to do to work around this is create your own attribute in the Custom Item Specifics section to accomplish the same thing by entering the name of the attribute in the "Detail Name" field, entering the size in the "Value" field, and then clicking the "Add" button.
As long as you still select something from the "Size Type" menu and call your custom attribute something other than just "Size", such as "Sweater Size", I believe that the information may make it to eBay in the Item Specifics section, although I have not tested this out personally.
I hope this helps. If you need any further assistance with your account, please feel free to contact our customer support team by mousing over the “Help” tab and selecting the “File a Support Case” option.
-Mike
