advisor / adviser
Two spellings of the same noun.
Both adviser and advisor are standard. Adviser is the older and still widely used spelling. Advisor is common in job titles and institutional names. Choose one spelling for a document and keep it, except when a proper title is fixed the other way.
Examples
UseShe is a faculty adviser.
UseHe works as a financial advisor.
Avoidmixing adviser and advisor for the same role in one article
Neither spelling is a mistake. Titles and letterheads decide themselves. The above is our guidance.