You have irregular cash flows and as such, you don’t always make the amounts for the due dates. Needless to say that it’s possibly poor cash flow management from your part, but it also begs to question which would make more sense – to pay up partly or wait until you can make a full payment to your supplier.

First things first, I would make it clear with the supplier who is the counterparty why such a situation arises in the first place, if it’s a permanent situation and how do you plan to ensure they will still get the money. It’s not just letting them know, but also agreeing that it’s acceptable for them aswell. It’s about agreeing on the situation and provided you’re interested in the services and / or goods, you do really want to do that. 

Now as for the options on whether to pay in parts or later in full, if not specificly mentioned or asked by the supplier, consider which you yourself would prefer. Most probably, if you’re having problems with managing your cash flows, it would make more sense to actually pay in parts because of two reasons: 1) you have money right now, so pay what you owe; 2) paying part of what you owe, takes the stress of from your balance sheet as well (less of liabilities) and proves you’re creditworthy (and not unable to eventually pay up).

I would still say that it should be your goal to get our from such a situation where you cannot pay to your suppliers in full and in time. You should be working towards it either by better managing how your clients pay to you or optimizing your stock levels for an example .