plan 1 distribution receipt each month

Dear Experts,

Via a STO - We receive bulk material in a ship from the US that only sails once per month.How do you set up APO to plan 1 distribution receipt each month? I added calendars but this did not work as it must only constrain the production plan.I altered the capacity but this did not work either.   In MAT1 I have set the SNP procedure on the lot size tab to 28 days but it did not create the plan we need.

Please advise this product sell once per month