How to redirect to the checkout page after login (wordpress)?

Solution:

You can use woocommerce_login_redirect hook.

function wc_redirect_login( $redirect, $user ) {

    $redirect_page_id = url_to_postid( $redirect );
    $checkout_page_id = wc_get_page_id( 'checkout' );

    if( $redirect_page_id == $checkout_page_id ) {
        return $redirect;
    }

    return wc_get_page_permalink( 'shop' );
}

add_filter( 'woocommerce_login_redirect', 'wc_redirect_login' );`

You can also try WooCommerce Login Redirect plugin to customize redirects.