During my Facebook live on August 30, 2021, I shared 2 ways to create a pocket inside your card. One by using a longer than 8-1/2" piece of cardstock and the other by adhering a patterned paper pocket to the edge of the inside of the card.
Using a Longer Card Base
Using just card stock, start with a piece that is 5-1/2 X longer than 8-1/2". The length beyond 8-1/2" will be how wide your pocket will be. So if you use a piece that 5-1/2" X 9-1/2", your pocket will be 1" wide. I'd probably use a piece no smaller that 10", for a 1-1/2" pocket.
The gray lines show where to place your adhesive.
I punched a notch on the pocket so the recipient could more easily remove the contents of the pocket. I show that in black.