An accidentally ignored LinkedIn invitation cannot be pulled back, but nothing is lost. LinkedIn's help page on managing invitations says Ignore removes the invitation without accepting it and without telling the sender. They may invite you again, and you can invite them. The choice that does close a door is the one LinkedIn offers right after Ignore: I don't know this person.
What your choice did
Ignore only. The invitation is gone and the sender was not told. Invite them yourself, or wait for them to invite you again.
Ignore, then I don't know this person. That member can no longer invite you, and LinkedIn takes it as feedback on their account. If you do know them, your own invitation is the way to put it right.
Accept, when you meant to ignore. You are now 1st-degree connections. Remove the connection, which LinkedIn lets you do at any time.
Replied to the invitation's message. A reply does not accept the invitation. Go back to your invitations and accept it there.
How to read the decoder
For this case the decoder says one try is worth it. That means one invitation, sent by you, one time, not a new one whenever the first sits unanswered.
Two symptoms beside it show the same moment from the sender's side. An invitation still pending after weeks is what an ignored invitation looks like to the person who sent it, because LinkedIn never tells them. A withdrawn invitation that cannot be sent again is what happens when a sender takes one back to try a second time. Pick the one that matches your screen.
What to do next
Search for the person by name and open their profile.
Press Connect once. If Follow is their main button, Connect sits under More.
Add a short note if your plan allows one. Saying you meant to accept their invitation is enough.
Then leave it. If your invitation sits pending, do not withdraw it to send again: a withdrawn invitation blocks a new one to the same person for a while.
Sending your own invitations? An invitation nobody answers is no reason to send another. In a Oneprofile sequence, a new connection request comes with a withdraw step for the people who never accept, so unanswered invitations do not pile up.
