by-email.php
Line 970
$accept_link = add_query_arg( array(
'iaaction' => 'accept-invitation',
'email' => $email,
), bp_get_root_domain() . '/' . bp_get_signup_slug() . '/' );
$accept_link = apply_filters( 'invite_anyone_accept_url', $accept_link );
That’s where it’s set.
Change bp_get_root_domain() . '/' . bp_get_signup_slug() . '/'
to bp_get_root_domain() . '/yourpage/