It seems very inconsistent whether the embassy sends out a P3. Does your case say "Ready" through the CEAC status page?
You can go ahead and submit your DS-160, create an account on https://ais.usvisa-info.com/, and through that portal it will give you payment instructions for in-person payment at Abyssinia Bank. You will need to bring a payment document that is specific to your case number, which you will receive after making an account through that site.
NYandHEZ got a reaction from Chancy in K1 Visa help in Ethiopia [merged threads]