Q. What’s the difference between Onegaishimasu and Kudasai?

A. Both kudasai and onegaishimasu roughly mean “please” but there are some differences in usage. Kudasai has two meanings, verb “please give me” and auxiliary verb “please”. .
1️⃣
Kudasai as verb literally translates “please give me”. This kudasai can be replaced with onegaishimasu when you are ordering/buying something.
This kudasai is equivalent to “please” in the case below. .
👨🏻‍🍳“What can I get you ?”
👩🏻“Two beer🍻 and french fries 🍟, please.” .
2️⃣
Kudasai as auxiliary verb literally translates “please”. It has to be used with verb.
This kudasai is equivalent to “please” in the case below. .
👩🏻“My fries are not salty enough. Please put some extra salt.”
👨🏻‍🍳“No problem. Please wait and I’ll get you some salt..” .
3️⃣Onegaishimasu is polite form of verb “negau” meaning “to wish” so it literally translates “I wish”. You can use this by itself without adding any other phrases or words. You can replace “please” with “onegaishimasu” in the script below. .
👩🏻‍🍳“Can I get you another drink ?”
👩🏻“Please ! I’ll have another beer🍺.” .
And two hours later... .
👩🏻“Hey, one more beer🥴!”
👨🏻‍🍳“You had enough. No more beer for you !”
👩🏻“Oh no. Pleeeeaaaase !” .
.

In this case, you are begging, no longer wishing, but you can still say onegaishimasu to show your strong desire !