Inasmuch as I am running late with my calculations, I decided to pay a guesstimate payment using the app IRS2GO on my Android phone. When it came to asking for country of residence, it only gave a small selection of countries, none of which was what I needed.
I then went to directpay.irs.gov and successfully completed my transaction. My question, just for curiosity as I had bypassed the problem, was I doing something wrong or was IRS2GO?