YOU SAID:

Sunday is supposed to be a day of rest

INTO JAPANESE

日曜日は休息の日になるはずです

BACK INTO ENGLISH

Sunday should be a day of rest

INTO JAPANESE

日曜日は休息の日でなければなりません

BACK INTO ENGLISH

Sunday must be a day of rest

INTO JAPANESE

日曜日は休息の日でなければなりません

BACK INTO ENGLISH

Sunday must be a day of rest