Goodwill is using technology from PayActiv, a start-up in San Jose, Calif., that uses employers’ wage and hours information to estimate their employees’ earnings. For a fee of $5 per transaction — of which Goodwill pays half as a courtesy to its workers — PayActiv advances the cash. On payday, it recoups the money directly from the employer. PayActiv’s founder, Safwan Shah, talks with a missionary zeal about the potential impact. “The biggest bank in this country is the bank of the employer, and two to three weeks of salary for most people is stuck there,” he said. “This is a corporate responsibility issue.”