How do manager increase employee motivation when they feel they are underpaid?

Salary is not the only thing that motivates employees to work for a company. Mostly, people care the working environment. Manager can do his best that is in his control. Manager should assign challenging tasks, delegate more responsibilities that will make those employees learning new skills/things, hold frequent team building activities, provide travel opportunities to customer site, Praise the good work of team members in team meetings, arrange training to the team members, hold frequent one-o-one discussions to review career path and guide them, etc.. These will help to motivate the employees. 

Implement a performance bonus and perhaps choose a person who is the staff of the month. Have a rewards program so that those who work hard have a goal to work towards. They become more productive if staff meetings are held on a regular basis. Use those meetings to keep the staff motivated and remind them of the rewards they stand to gain if there performance meets expectation. 

conversation, friendly, god works place, congrate them, show them  what the futur will bring

We need to motivate, what the failures and challges we are faced, and we need to be with to complete the sales.

salary is not the only thing that motivates employees to work for a company mostly people care the working environment manager can do his best that is in his control manager ... By delegating important assignments and responsibilities he will feel more valued and feeling of underpaid and neglect wont creep his mind.

Manager needs to be adviser,guide counsellor and Mentor. By delegating important assignments and responsibilities he will feel more valued and feeling of underpaid and neglect wont creep his mind.