"जन्मदिन की शुभकामनाएँ। मेरी शुभकामना है कि आप हमेशा ख़ुश रहें।" "Janmdin ki shubhkamnaen. Meri shubhkamna hai ki aap hamesha khush rahen."

Thank you Yusuf. Could you write down how to pronounce the sentence?

You can say "जन्मदिन की शुभकामनाएँ। मेरी शुभकामना है कि आप हमेशा ख़ुश रहें।" शुभकामना means good wishes, so in Hindi we actually say good wishes on your birthday. ख़ुश means happy, so the next sentence says I wish you always be happy.