Unable to Transfer to Another World

I have a friend who has a character on Excalibur and she wanted to transfer to Ultros. She told me Mogstation was preventing her because of this:

"This character or one of its retainers is in possession of a ceremony invitation."

She told me she got invited to a wedding that never happened so she threw the invitation away, and she did not own any retainers and her inventories (including Saddlebag) were not containing it. She had contacted SE but no help was given.

Would appreciate if I could find a solution here.

Then they are still in possession of the item. Try an /itemsearch in the game, also check expired retainer contracts that may have it or the moogle mail box will also prevent you from moving if its in the mail.