How do you say happy monthsary in using mandarin?

In Mandarin, "happy monthsary" can be expressed as "祝你们的月庆快乐" (zhù nǐmen de yuè qìng kuàilè). "月庆" (yuè qìng) means "monthsary," and "快乐" (kuàilè) means "happy." You can also simply say "月庆快乐!" (yuè qìng kuàilè) to convey the sentiment directly.