For enabling Online Payment by Customer, Payment Gateway must be added into neuCRM on Admin → PG menu.
There you may find some Payment Gateway service provider, which was already integrated
You can choose one of the Payment Gateway service provider, and add your Payment Gateway.
Inorder receive Payment online, atleast one payment Gateway must be configured
And Finally set portal_online_payment=Y on Configuration to Enable Online Payment.
If you can't find your required Payment Gateway Service provider on this list, please contact our support team we will do the intergration for you.