Why a one-line birthday message stops working
The first version of every birthday invitation is a text: Saturday, my place, seven o'clock, come. It is honest and it is quick, and it works perfectly for about six people. Past that number the chat becomes the guest book, the menu query desk and the lost property office all at once.
Somebody asks what time to finish. Somebody else asks whether partners are included. Two people ask what they should bring and you answer both in different threads with different sentences. Then the headcount you need for the food and the drinks is a rumour, and the person who said something vague three weeks ago is still an unknown.
An invitation page does the same job as your message, only once. You write the plan on the page, send the link into the chat, and everyone reads the same version. The reply button underneath is where the answering happens, which keeps your thread free for the part that is actually fun.