I had, and I am still dealing with, a similar experience with a carpet python. His shipment was delayed/lost and he got to me much later than anticipated. Within a day, pops, and within two days, wheezing and mucus coming out of the nose. Not good.

Stress from shipping, or anything else, can cause them. If you catch early, there is hope. Make sure you go to a reputable vet who does a tracheal wash/flush to determine what's causing the RI and bacterial, what bacteria, so they know what to prescribe.

Yafe, my carpet, is on his second antibiotic, and it's being given to him via nebulizer, and he's slowly, but surely improving.

Also, probably goes without saying, but he's being properly quarantined, correct? Simple enclosure, as bcr229 said, but also being kept away from other animals, handled last, or clothes changed and extra hand washing, etc. if you have to go back to another animal, separate tools (feeding tongs, hooks, etc.), hides, bowls, etc.?