Paypal stays in Sandbox mode

Hello,
I am having some issues with the PayPal integration in a Form.
it doesn't matter if I use a Sandbox ID or Live ID, when I have filled in the form and go to Paypal, I always see in the URL the Sandbox mode.
Initially, a Sandbox ID was entered. I have changed it to a Live ID, but the URL still displays 'Sandbox'. I’ve tried using different browsers, but the issue persists. Could you please assist me?

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