There are several parameters that KA includes into ISV requests to the ISV endpoint for backward compatibility purposes. These parameters can actually be ignored:

Name Size (Characters) Description
APS_PROTOCOL_FAMILY 3 Always equals APS
APS_PROTOCOL_VERSION 1 Always equals 3
APS_CULTURE_ISO_CODE 5 Always equals en_us
RUNNING_NO 1 Always equals 1
QUANTITY 1 Always equals 1
ENCODING 4 Always equals UTF8
LASTNAME 5 Always equals Plesk
FIRSTNAME 5 Always equals Plesk
COMPANY 5 Always equals Plesk
EMAIL 19 Always equals blackhole@plesk.com
PHONE 12 Always equals +41315281223
FAX 12 Always equals +41315281223
STREET 14 Always equals Vordergasse 59
CITY 12 Always equals Schaffhausen
ZIP 4 Always equals 8200
STATE 0 Always equals empty string
COUNTRY 11 Always equals CH