It’s secure building and Recipient does not answer the intercom
There is a little trick that a lot of Runners find helpful, you could try to ring the neighbours on the intercom and explain that you have a delivery for the correct unit number. A lot of times, you will find out yourself passing the security this way. Still no luck? Please call Sender and/or Recipient and ask them if they want it to be returned. Please make a note in the comments section, so a redelivery fee or a return fee can be calculated where applicable.