How were Black People prevented from voting despite the 15th amendment?

The 15th Amendment gave minorities the right to vote and the passing of The Voting Rights Act of 1965 addressed literacy tests and violence that often prevented African American voters from exercising that right. However, it is believed that racial Gerrymandering continues to be an issue that leads to violations of equality in voting. Gerrymandering is the process of drawing district or precinct borders in such a way that people of a particular ethic group, party affiliation or socioeconomic structure are either advantaged or disadvantaged unfairly during voting. In 2016 in the case of Bethune-Hill vs. Virginia Board of Electors, was heard by the Supreme Court of The United States. The case was presented by Golden Bethune-Hill on the basis that the way that 12 districts drew their voting lines, caused an unfair disadvantage to African American voters. While 1 district was upheld as drawn, 11 of the other districts charged were returned for further proceedings in the United States District Court for the Eastern District of Virginia. The findings showed that while race was not the only factor in the creation of an unfair advantage, it could have been a factor. The reality that it was possibly a factor could cause voters to question the fairness of their representation. It is measures like these that indirectly dissuade voting among African American populations.FURTHER READING:https://www.britannica.com/topic/gerrymanderinghttps://www.supremecourt.gov/opinions/16pdf/15-680_c07d.pdfhttps://www.oyez.org/cases/2016/15-680

Though the 1870 Amendment to the U.S. Constitution granted African American men the right to vote, mechanisms like literacy tests and poll taxes prevented many from doing so. Moreover, employers, white mobs, and organizations like the Ku Klux Klan used threats and intimidation to keep African American men from the polls.
In Mississippi, for example, a poll tax had to be paid two years before a scheduled election per the state's Constitution; this prevented many from voting. Literacy tests included tasks such as reading a part of the state's Constitution and explaining it to the county clerk, at whose discretion the prospective voter would be deemed literate or illiterate. Literacy tests for white men were generally much simpler, to assure their success.
Some states required voters to own property, and fewer African Americans than whites were able to meet this requirement. Some states did not allow anyone who had been arrested to vote, and often, African Americans were arrested on trumped-up charges for this reason. And lastly, some states would occasionally purge the lists of registered voters, only allowing re-registration after an important election.
https://abhmuseum.org/voting-rights-for-blacks-and-poor-whites-in-the-jim-crow-south/

https://www.crf-usa.org/brown-v-board-50th-anniversary/race-and-voting.html