easy, you should encrypt the sensible letters or signs with other signs and let the receiver know what are the characters swapped in short give him the key. It worked since ages, and cryptographic world was up and at its best during wwii with enigma, the electromechanical nazi machine the british took years to decrypt. It was really complicated because it had several cross passes, I'm just showing you how easy to encrypt a simple link on airbnb with one simple pass (you have to follow this if you just want to give your guest more information and not giving out your link to let the guest book directly with you).
A) take your link and pass it on google shortener
B) now you have a short link, replace the g with another letter such as z, the dot with a sign (say -) and the slash with a sign (say +), put spaces in between
C) give your guest the encrypted string, at same time under the string give him the key to decrypt your link telling him to replace the z with g, the - with the dot and the + with the slash and strip out the spaces.
work great, try it 😉