Can I link multiple SIP Orders to the same mandate?

Yes, you can link multiple SIP Orders to the same mandate. In order to do that, simply create a new SIP order and in the Autopay section, select the pre-existing mandate you have approved earlier. 

In case the Autopay mandate is approved using UPI, the maximum amount to be debited cannot exceed ₹15,000. In case you want to invest more, you need to create a new Autopay using net banking as explained in the above point.