Think not easy such customer service. That's like asking the delivery hiong.
If its single block condo still ok to anyhow humtam a unit number. But if there are mulit-blocks, not easy. As each block unit number is different. The security may check and know one if anyhow humtam.
But lift lobby still okay bah. Some security may be quite chin chye one, will allow in, but not all. But think usually for condo, its either access with the unit number or wait outside customer come collect.
But if the delivery hiong and do above, then risk is on the delivery bah. Not many will hiong. Waste time don't say. Might as well just follow protocol, try contact and if cannot then just leave the food somehere and take photo info.
Although, the lift lobby is quite an option, especially in condo with many blocks. Can just leave order on the mail boxes (usually inside or somewhere near lift lobby), if customer cannot be contacted and don't have unit number. Throw is the last resort. Which think not usually do. Since can still leave near lobby and take photo.