Can I see the customers who started a booking on my portal but did not pay, so I can call them back?

Yes, in most cases you can see the bookings that were started on your portal and never paid for, and those are usually the best follow up calls you will make all week.

When a customer fills in their details and then drops off at the payment step, that attempt is normally still sitting in your admin area with a status showing it was not paid or that the payment failed. You can see the route or the hotel they were looking at, the travel dates and the contact details they typed in, which is enough for one of your staff to ring them and finish the sale over the phone. The same is true of any enquiry or callback form you put on the site, as those come into the same place for someone to pick up.

Where it stops is with the visitor who only searched and then closed the window. That person never gave you a name or a number, so there is nothing to call, and no honest system can tell you who they were. You will see that traffic as visits in your website statistics, but not as people. It is also worth remembering that the rules on contacting customers differ from one country to another, so a follow up call or message needs to sit inside whatever applies where you trade, and how much of this you can see depends on your plan and how your portal is set up.

Have a look in your admin for the list of unpaid or failed bookings, and make working through it a daily habit for one person rather than something you check when you remember.