What does-138*50* 10 mean?

138 stands for "get rich all your life". Good luck in your life. 138 is homophonic with "lifelong hair" to express the blessing to each other in disguise, also for good luck. Common red envelope numbers are 108 (for sure), 168 (for all) and so on.

The Chinese phonetic homonym of the number 50 10 is obviously "kiss you and want you", because boys really like you as a girl, so if you want to kiss a girl affectionately, you have to marry a girl.