Payment Types

The Paymaster supports three payment types that provide flexibility in how gas fees are handled. Each type offers different benefits and trade-offs.

Type 0: Free Gas (Sponsored)

The developer fully sponsors gas fees for the user. This is ideal for:

• User onboarding
• Promotional campaigns
• Simplifying UX
• GameFi applications

To use this type, set type: 0 in your context object when calling pm_sponsor_userop.

Type 1: Prepay with ERC20

Users pay for gas with ERC20 tokens before transaction execution:

1. The full estimated amount is collected upfront during the verification phase
2. Excess is refunded after execution
3. Requires token approval before transaction

To use this type:

• Set type: 1 in your context object
• Include the token address in your context object
• Ensure the user has approved the Paymaster contract to spend their tokens

Type 2: Postpay with ERC20

Users pay for gas with ERC20 tokens after transaction execution:

1. Only the exact gas cost is collected after the transaction completes
2. Requires token approval before execution
3. Better UX as users only pay what’s needed
4. Has a risk of payment failure after execution if the UserOperation depletes tokens

To use this type:

• Set type: 2 in your context object
• Include the token address in your context object
• Ensure the user has approved the Paymaster contract to spend their tokens

Choosing the Right Payment Type

When deciding which payment type to use, consider these factors:

• Type 0 (Free): Great for new user acquisition, but increases costs for the developer
• Type 1 (Prepay): More reliable but requires users to have slightly more tokens than needed
• Type 2 (Postpay): Best user experience but comes with failure risk

Most applications use a combination of payment types - offering free gas for first-time users or specific actions while using token payments for regular operations.