Product Category Code?

I just upgraded from v.3 to v.4 and on the sign up page of my various websites, every product that I have is showing up instead of JUST the product related to that specific website.

I want to specifically limit which product shows up on different order forms, and it needs to be different for each website.

In v.3 you could assign a "price group number" to a product and in the html code for the sign up button on my website, I could create the link following link to show JUST that product when the customer went to sign up:

http://www.mywebsite.com/amember/signup.php?price_group=-2

In v.4 there are now Product Categories, and forms, which I see has a much greater flexibility than the price group method. I see that I have to generate a code. However, I can't for the life of me figure out what I need to put in the html code on the sign up button.

I generated the code following code:

iCP0z4hj2L

I put it in the link below, but it did not work. All products are still visible.

http://www.mywebsite.com/amember/signup.php?iCP0z4hj2L

What do I need to do to my html sign up button (or aMember) so that ONLY the correct product shows up when signing up?

Any help would be greatly appreciated!

I found some helpful info in another thread and then finally pieced it together.

Under the forms editor, when you add a new form, you will need to drag the "Brick" called "Product" from "Available bricks" over to the "Form Bricks" column.

Once it is there, click on it and a product configuration window will pop up.

You will need to have already created a category and assigned your product to that category.

For "What to Display" select "products from selected categories" and then add the product category on the next line below.
After you do that, click "OK" . Return back to the Forms Editor, where you will see a list of all of your forms. The second to the last column on the right is "URL"

For the above example in the above post, it says "signup/index/c/rRCB0LEi"
so I added this link to the signup button and it works:

http://www.mywebsite.com/amember/signup/index/c/rRCB0LEi