Open the following ports on your firewall for TCP/IP traffic inbound and outbound:
SellerDeck Desktop version 18
54387 and 54388
SellerDeck Desktop 2016
54385 and 54386
SellerDeck 2014
54381 and 54382
SellerDeck 2013
54377 and 54378
v11
54375 and 54376
v10
4373 and 4374
SellerDeck Epos
4370
SellerDeck Desktop version 18
54387 and 54388
SellerDeck Desktop 2016
54385 and 54386
SellerDeck 2014
54381 and 54382
SellerDeck 2013
54377 and 54378
v11
54375 and 54376
v10
4373 and 4374
SellerDeck Epos
4370