Looking on the internet deeply has found these results:

invitation to the party is the most popular phrase on the web.

invitation at the party 162,700 results on the web	invitation to the party 16,380,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
I got your invitation for the party this Weekend. It'll serve as his invitation for the party tonight. When we landed, my representative in Russia asked to see an invitation for the party to make sure that everything was on schedule. The party's for a bunch of environmentalists, so I found a guy downtown who makes biodegradable party invitations that can also be used as toilet paper. I used it for the party invitations. You accept an invitation to a party at the home of my sworn enemy, he tells everyone we're going to be there, and when we don't show, he looks the fool. If it's okay, we'd also like the invitation list to the party.	What's in the envelope must have been the invitation to the party. Look, I appreciate the invitation to the party, but I've already told the police everything I know.

invitation at the party

162,700 results on the web

invitation to the party

16,380,000 results on the web

More popular!

I got your invitation for the party this Weekend.
It'll serve as his invitation for the party tonight.
When we landed, my representative in Russia asked to see an invitation for the party to make sure that everything was on schedule.
The party's for a bunch of environmentalists, so I found a guy downtown who makes biodegradable party invitations that can also be used as toilet paper.
I used it for the party invitations.
You accept an invitation to a party at the home of my sworn enemy, he tells everyone we're going to be there, and when we don't show, he looks the fool.
If it's okay, we'd also like the invitation list to the party.

What's in the envelope must have been the invitation to the party.
Look, I appreciate the invitation to the party, but I've already told the police everything I know.