There are some mistakes in your form:
1. The page must be php and not html.
2. The form has no action at all. The action should be the page itself: "dform.php"
3. Encoding type: it is set to text / plain, must be multipart / form data
4. You need Radio buttons, not checkboxes because only one ammount should be chosen.
5. These radio buttons should have the same Group name (at the moment they are unnamed)
6. You do NOT have the "If "statement so hat the button will only appear after a selection has been made.
7. You did not define any item name, item value etc when creating the button. Also no return page. Did you create it in PayPal, or did you use BV's PayPal tool?
8. You did not replace the item name and value (which do not exist) with the php code as per tutorial.
Please read again and follow the instructions.

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