I solved this puzzle
ignore it :p

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I told hot dog(?) vendor that move location to mosley's office and went to there
But since i failed to sneak in office, Vendor is not coming any more!
Is it bug something? Because of it, I can proceed this game

Please help me

You have to wait for Frick to fall asleep.

Sometimes you have to leave and come back. The vendor will be gone, but Frick will still eventually fall asleep and you'll have enough of a window to get into Mosely's office.

Stupid puzzle I know