After testing, we found that this is a bug in renpy version 8.3.2. Checking the official renpy update announcement, we found that this bug has been fixed in the new version 8.3.3 (Fixes). The achievement.steam.get_session_ticket() function now works as documented.) We've addressed this issue by updating to a newer renpy version that now fixes the achievement issue in version 0.2.1 and later of the game, thank you for your support! Thanks!