nobody would like to spend 20mins to answer the survey unless we pay money to them.
it's important to get a good quality survey result.
the most popular payment in the world is paypal and alipay.
i am not sure if LS already has this function to pay money to participant.

No, the payment usually is either done by the panel provider or after the survey has finished manually.

Limesurvey does not have such a function and to be honest I personally wouldn't want a automatic payment function at the end of my surveys, because while you sleep some evil hacker might empty your bank account...

It should not be too difficult to track completes and send Paypal payments to them in a batch later.

You could ask for email addresses, and after your survey is complete - filter out any 'suspicious' responses i.e chinese using a VPN and then send out amazon vouchers. Some people don't have PayPal accounts, and even if they don't have an amazon account, they can simply create one to redeem their voucher afterwards.

actually,i tried to use amazon vochue, but the feedback is not attactive as paypal,alipay.the largest payment company.
i don't use the panel provider because the high cost and i cannot control the quality.
i tried other system, when you finish survey, you will get 3 points or 5points, when you have 10 points, you input your paypal,alipay account, then you will get 10$.
as ls has no such function, i am not sure if i can use a plugin to do it.

A plugin can surely do this, but it's a real development task.

www.limesurvey.org/en/community-services...type-question#113780