Business visa or work visa

Hi,

I work for a UK company that has been hired by an Omani company to provide technical assistance to them for a couple of days. I am trying to find out which visa is appropriate for this situation. I am not directly employed by the Omani company and will only be working for 48 hours. They are desperate for me to arrive quickly but there does not seem to be enough time for them to provide a work visa, they have told me to get a visa on arrival at Muscat airport.

Is this legal?
What is the punishment for working on a visit visa?
Is a buisness visa better?
Or do I need a full work visa, even for such a short time?

Thank you in advance!