Does AWS MarketPlace require additional payment methods or is it optional?

AWS Marketplace does not require additional payment methods beyond what you've already set up for your AWS account. The payment method you established when creating your AWS account is used for AWS Marketplace purchases. This can be managed in the AWS Billing and Cost Management console.

Regarding your specific situation, it appears that you have already provided some of the required information, including tax information and a SWIFT bank account. However, the error message you're receiving suggests that there might be an issue with the disbursement information.

For sellers on AWS Marketplace, especially those offering SaaS products, it is indeed required to provide complete financial information before you can submit a product. This includes:

1. Tax information (which you've completed)
2. A registered bank account (which you've provided)
3. Disbursement preferences

The disbursement preferences are a crucial part of the process. As a seller, you need to set up how you want to receive payments from AWS for your product sales. This involves choosing between daily or monthly disbursements and selecting the currency for your payments.

To resolve the error you're encountering, you should:

1. Sign in to the AWS Marketplace Management Portal
2. Go to the Settings section
3. Select the Payment information tab
4. In the Disbursement methods section, add or edit your disbursement preferences
5. Choose your preferred currency and link it to your bank account
6. If opting for monthly disbursements, select a day of the month for processing

Even though you've updated your bank and tax information, the system may require you to explicitly set up your disbursement preferences before allowing you to submit your SaaS product.

If you've completed all these steps and are still encountering the error after a reasonable processing time (which can be a few business days), it would be advisable to contact AWS Marketplace support for further assistance.

Sources
Paying for products in AWS Marketplace - AWS Marketplace
Disbursement preferences for AWS Marketplace sellers - AWS Marketplace
SaaS product guidelines for AWS Marketplace - AWS Marketplace