A firm has offered me a job in Ghana. They have requested that I pay a sum of USD 1200 required to process a work visa for me. Is this generally in order?

I don't think so... Before sending $$, please do yourself a favor.. write to US embassy in Ghana and ask the same question.

Follow this link: https://www.askmehelpdesk.com/visas-passports/ghana-passport-visa-fraud-288039.html

Sounds like a scam to me

Don't send any thing,there r lot of online fake because.dont do any thing in hurry.get company website address and then call them about your appointment