Region lock.

AD AE AG AI AQ AS AT AU AW AX BB BE BG BH BL BM BQ BS BV CA CC CH CK CW CX CY CZ DE DK EE ES FI FJ FK FM FO FR GB GD GF GG GI GL GP GR GS GU GY HM HR HU IE IL IM IO IS IT JE JP KN KR KW KY LC LI LT LU LV MC ME MF MH MQ MS MT NC NF NL NO NZ OM PF PL PM PT QA RE RO SA SB SE SH SI SJ SK SM SX TF UM US VA VC VG VI WF YT

Giveaway was posted once without region lock info, winner saw key and notified me about restrictions.