The best and simplest way is to create a URL Token. Make sure you enter:

1. Merchant Facility
2. Payment Form
3. Campaign

After saving the URL Token, you can copy and use the Full Text URL link

Steps to create

1. Click on the URL Tokens Tab. (If you cannot locate this, click on the 9 dots in top left corner, then search "URL Token"
2. Press New button
3. Select a Merchant Facility
4. Select a Payment Form
5. Select the Campaign
6. Save

After Saving, copy the Full Text URL and use that for your emails or website