Please pay your membership fee by the 20th of each month for the following month.
Membership fees must be paid by the 20th of every month for the next month.
ーPlease pay your membership fee by the 20th of each month for the following month.
「毎月２０日までに翌月の会費を払ってください。」
membership fee で「会費」
by the 20th of each month で「毎月の２０日までに」
following month で「翌月」
ーMembership fees must be paid by the 20th of every month for the next month.
「翌月の会費は毎月２０日までに支払わなければいけません。」
by the 20th of every month で「毎月２０日までに」とも言えます。
for the next month で「翌月」
ご参考まで！
カナダ 
