Paypal Adaptive payments don't work anymore.
 https://developer.paypal.com/docs/archive/adaptive-payments/

Your seller clicks on a sign-up link on your website which redirects them to PayPal for sign up. After completing sign up, your sellers are ready to start taking payment.

Before integrating upfront onboarding, you must be an approved partner, and you must have an access token. Then, complete the following steps:

1. Make a Partner Referrals API call.
2. Add a PayPal sign-up link on your site.
3. Seller signs up on PayPal.
4. Redirect the seller back to your site.
5. Track seller onboarding status.

But there'is an alternative...  https://developer.paypal.com/docs/commerce-platform/onboarding/upfront/

https://wedevs.com/18319/paypal-adaptive-payments-add-dokan/

 https://docs.woocommerce.com/document/woocommerce-shortcodes/