PayPal Express Checkout Not Working

[ramguiao]

Hi,

I followed every tutorial you have to correctly integrate the PayPal Express Checkout to my website. Unfortunately, I can't make it work. I am having this message "The transaction is not valid". I am sure that I have the correct Sandbox API key. Please let me know how can I resolve this. Thank you so much!

[MTS_Justin]

Hello,

Check the URL shown in the address bar, you're posting to "www.paypal.com", but if sandbox testing you should be posting to "www.sandbox.paypal.com".

Correct the endpoint where you're submitting the request to and retry.