Is it permissible to work in a job that includes accounting and sales responsibilities, even though the experience certificate submitted to obtain the visa is for a "marketing specialist"? And is the money earned from this work unlawful?

There is no objection to obtaining a certificate of experience under the title "Marketing Specialist" and using it to obtain a work visa, for the following reasons: your work includes accounting, sales, and marketing, and there is no objection to obtaining a certificate under the name of one of the tasks you performed. Furthermore, the department you worked in was "Sales and Marketing," and sales and marketing work are intertwined. The company requesting your recruitment is fully aware of the details of your CV, and no deception has occurred. Even if there were a discrepancy in the title of the "visa," this does not mean that the work or salary is prohibited, as long as your work is within permissible bounds.