I am confused with the role of "that" and the clause that follows in the passage below. Is the "that-clause" grammatical here? If no, how should it be put in a grammatical manner? If yes, what is the grammatical role of "that" (like complementizer, relative pronoun? ) and how to analyze the structure of the clause?
"[...] In 2005, Iceland’s pay gap showed that women were, on average, still being paid only 64.15% of what men earned. So, on the thirtieth anniversary of the Women’s Day Off, women organized another strike and left work at 2:08 p.m., shortening their workday by the exact percentage that their salaries were lower than men’s. In 2016, women in Iceland again left work early, this time at 2:38 p.m. [...]"
Your help and clarification are much appreciated! 😇