Is the accountant obligated to pay for the refreshments and biscuits he provided to the workers after the employer prevented him from doing so, especially since the supervisor ordered him to provide them, and if providing them serves the interest of the work, does the obligation to pay fall away from him?

As long as you informed your employer of what you purchased and he did not ask you for its cost, then nothing is incumbent upon you. And if you relied on the opinion of the supervisor and he was authorized, then nothing is incumbent upon you. However, if he was not authorized, then the purchase takes the ruling of the unauthorized agent's action, which is suspended upon the owner's approval.