Visiting Facebook help center will let you know the right way to know How To Link Cash App To Facebook in a proper manner.What you need to do is to implement the instructions that are available over there and you will be able to get your card linked with your Facebook messenger.
Steps to link a Cash App card to Facebook messenger-
First open Facebook messenger on your phone.
Now from the top right corner tap your profile icon.
After that from the drop down menu, you need to select the payments tab.
Here comes a screen where you can see your already added debit cards.
Greeting,
Rachel Gomez