There are a number of reasons why you might not be able to find a match.

If a player sends out multiple match requests, the first one to respond will enter a game with that player, others who accept the invitation will receive a notification saying that the player requesting the match is unavailable. You might also receive a notification letting you know your match is unavailable if either you or that player is temporarily disconnected from the app.

To avoid this please refrain from inviting multiple matches to play at once, and verify that you have a stable connection before sending or confirming match requests.

Should you miss an important invitation that you wanted to accept, you can always send a request back to that person. Do so by accessing your Ludia inbox to find the player you missed. Select the profile from the recently invited list and send an invitation to them through it.