United had reached an agreement with the Championship club over a move for the Welsh midfielder last week.
And the switch was made official on Wednesday with James signing a five-year deal at Old Trafford.
But Manchester United did not let the deal run smoothly.
They tagged the wrong Daniel James in an Instagram post as part of the announcement.
The original post wrote: “When @DanielJames_97 smiles, we ALL smile!”
However that Daniel James is not the new United signing though his follower account did rocket after the mix-up.
The post was swiftly edited to include James’s correct username – Daniel_James97.
But fans had already spotted the mistake from the Premier League giants.
One had responded to the post with: “Wrong tag bro!”
Another added: “Wrong tag”
A third wrote: “Re-edit the username”
With a fellow United supporter commenting: “That’s not the right Daniel”
Amazingly, United got the James tag wrong AGAIN on Twitter.
They tagged @Daniel_James_7 instead of @Daniel_James_97.
James enjoyed a stellar season in the Championship with Swansea, netting six goals and making seven assists.
The 21-year-old is Ole Gunnar Solskjaer’s first signing of the summer with the Norwegian keen to freshen up his squad.
And James can’t wait to get going at Old Trafford.
He said: “For me, it’s surreal, really.
“I think every kid grows up wanting to play for Manchester United.
“I never thought I’d be able to play against them, never mind play for them, so it’s surreal, and I’m really looking forward to it. I can’t wait to get started.
“I am looking forward to working with Ole, meeting the team and getting started.”