Im new to sun and moon and wanted to get milotic after i farmed a feebas. So i first went on gts but that didnt really work since you couldnt request items. And then i went to wonder trade and thought i would get more confirmation and options but in the end i traded a f(r)eebas with prismscale for a slowpoke. Feels bad. 🙃
Welcome to the forum! I'd love to make your next experience trading pokemon in Sun and Moon better. If it's okay I'm going to move this to thread over to the Trade section of the forum where I think you can get more support if you are still interested in Milotic.
Do not use wondertrade if you want back the pokemon you are trading, only use it for pokemon you intend to part with. Wonder Trade is meant to be a one-off with totally random people and pokemon.
Generally when you trade over the GTS it's understood as a one-time-trade as well, but since you can attach some conditions you can still use the GTS to make sure you get a Milotic. While you can't specify the items the pokemon you receive holds, you can specify what species of pokemon you want. The best way to go about acquiring a Milotic would be to type in "Milotic" as the pokemon you will are trading for.
Whether you deposit a Feebas with prism scale or a haunter, just require Milotic to be the pokemon you receive in exchange. Sometimes it can take a few hours or days for someone to find you, and take you up on your GTS trade, but if it is a fair trade, and you're not putting up Magikarp or a Yungoos, then you should be able to get a Milotic soon enough.
If don't want just any Milotic, but a specifically the Feebas you bred to evolve and be traded back to you then talk to a friend, and do a link trade with them. There are frequent traders here in the forum who can also help you with that, and might even need something traded back in return.
My username is VisionofMilotic. Milotic is my signature pokemon. I have dozens of boys and girls with 5-6 ivs, good natures and either ability just sitting around in my pokebank if you want one of mine. I don't need anything special in return.