This page is just a reference of all the known Steam APIs, I do not know how they work. Please do not email me with questions.
PUBLISHERPOSTReportAbuse
https://partner.steam-api.com/ISteamCommunity/ReportAbuse/v1/
NameValueTypeRequiredDescription
click to setstring Yes access key
uint64 Yes SteamID of user doing the reporting
uint64 Yes SteamID of the entity being accused of abuse
uint32 Yes AppID to check for ownership
uint32 Yes Abuse type code (see EAbuseReportType enum)
uint32 Yes Content type code (see ECommunityContentType enum)
string Yes Narrative from user
uint64 NoGID of related record (depends on content type)