I have a Xbox live subscription, but it won't let me play online multiplayer.

Thank you for letting me know. Do you have an Xbox Live Gold subscription? Because it is required to play an online multiplayer game.

I apologize but the game is an online multiplayer game which will require us for an Xbox Live Gold subscription.

Xbox Game Pass for console is a different subscription and it’s a subscription where you can access hundreds of Xbox Game Pass games on your console however it will not let you play online multiplayer.

That is exactly what I have been trying to do and it won't let me. It keeps telling me "You need an Xbox LIVE Gold Membership to play multiplayer games online. Would you like to become a Gold member today?"

You need Xbox Live to play online multiplayer. There are a lot of titles out there that do not require you to have live to play.

Playing on any gaming console online will require you to purchase a subscription to have access to the online multiplayer severs. PlayStation Plus is the same cost as Xbox Live, and they require you to have a subscription to play certain games online as
well.

I appreciate you letting me know. Do you have an active Xbox Live Gold subscription, Tanya? It is required to play an online multiplayer game. Kindly check:

Press the Xbox button on your controller to open the guide, and then select System > Settings > Account > Subscriptions.