So I have been battling with getting my emails looking all nice and pretty, and I have managed to make progress with applying headers and footers in SendGrid.

Whilst doing all this, I came across this post:

https://wpforo.com/community/how-to-and-troubleshooting-2/activation-link-is-broken-registration-key-is-invalid/

@Anonymous20 - you asked why there were <> around the link... well it is because it has been coded that way in wpforo:

$set_password_url = '<' . wpforo_home_url( '?wpforo=resetpassword&rp_key='.esc_attr( $key ).'&rp_login='.rawurlencode( $user->user_login ) ) . '>';

Interestingly, the reset_password_url doesn't have the same <>:

$reset_password_url = wpforo_home_url( '?wpforo=resetpassword&rp_key='.esc_attr( $key ).'&rp_login='.rawurlencode( $user_login ) );