I am now, have been and will be wrong

Do I call the potential customer/investor/partner?

If you have to ask, the answer is YES.
What's the worst that can happen?
Rejection? A "No"

Guess what,
It's not that bad.

Just "No"

Talk, ask, Find out what's going on. Even if it's an answer you don't like. It IS an answer.

Then, move on with the rest of your plan.

Never let your business live or die at the mercy of any one individual, supplier, customer, or investor.

"Not your fault" is cold comfort when closing out your business, and shutting the doors for the very last time.

When you're the best, everything is your fault.

Keep this customer, and the one you got last week, and the one you kept the week before that.
Find the next customer, and the next.
Find a second supplier, and a third.

Keep calling, keep asking. If everyone says no, something's wrong. If everyone says yes, something's wrong. Get enough yes answers and sales to keep the company around. Get enough no answers to know where you stand.

Pick up the phone.