Hello Riyas,

As of now there is no configuration to ask payment details on same page. If you want to ask these details on same page, then it will require customization in core. It will require significant changes.

You can skipe the login/register page using Oneclick Checkout plugin.
https://stackideas.com/docs/payplans/administrators/advanced/one-click-checkout

Let me know if you have any query.