I was expecting a `,` or a `}`

The error was detected in line 58, but its cause is before:

@article{balaji2012waterfall,
  title={Waterfall vs. {V}-Model vs. Agile: A comparative study on {SDLC},

The title value misses the closing curly brace at the end of the value:

@article{balaji2012waterfall,
  title={Waterfall vs. {V}-Model vs. Agile: A comparative study on {SDLC}},