The payment milestones for STP are as follows:

Payment for STP Processing Fees
You will need to pay the processing fee during the application stage. The eService for Student's Pass will prompt you that the application is "Pending Processing Fee." 
A: For prospective students of Institute of Higher Learning, please click this ICA e-Service.
B: For other prospective students, please click this ICA e-Service.
The available payment modes in the e eService are eNets; Credit/Debit Cards; Internet banking or PayNow.

Payment for STP Issuance/Visa Fees
If your application is successful, you will need to make payment for the issuance/visa fees. You can arrange to make the necessary payment once the status reflected in the relevant e-Service for Student's Pass is "IPA (Pending Issuance Fee)".
A: For prospective students of Institute of Higher Learning, please click on this ICA e-Service.
B: For other prospective students, please click this ICA e-Service.
The available payment modes in the eService are eNets; Credit/Debit Cards; Internet banking or PayNow.

Please refer to ICA website for more information on payment-related enquiries.

This information is sourced from ICA