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REF:

http://blogs.snapsis.com/PermaLink,guid,94277650-bd4c-445f-badf-b84646ecc8eb.aspx

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QUESTION:

When I add a PayPal Buy Now, Donate, Add To Cart, etc button to my DotNetNuke web site, the button simply refreshes the page, nothing happens.

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ANSWER:

1. Remove the <Form> </Form> tags from your PayPal code.
2. Add
onClick=”this.form.action=’https://www.paypal.com/cgi-bin/webscr’; this.form.submit();” 
to the Buy Now input button.

Example:
<input onclick=”this.form.action=’https://www.paypal.com/cgi-bin/webscr’;this.form.submit();” alt=”Make payments with PayPal – it’s fast, free and secure!” name=”submit” etc…


http://www.anysitesupport.com/how-do-i-add-a-paypal-button-to-a-dotnetnuke-web-site/