Switching parent to prepay

[lucky]

So long story short all of my parents pay me Monday for the upcoming week. All of them are consistent except one. The one family that was having a hard time. Mom has had some mental health issues and been out of the home. This parent has been paying every other Friday after services have been used, this is his pay schedule. The problem is he consistently "forgets" to pay me on this day. So I have decided he needs to start prepayment with everyone else. My question is how to go about it. Would you call personally, send an email, write an official letter? I honestly haven't really dealt with payment issues before and am at a bit of a loss.

[MyAngels]

I would call personally, then follow up with something in writing and have them sign that they understand the new rule. If it's too much of a burden to come up with the full amount at once, maybe have them pay something extra for a few weeks until they are paid ahead.