Mendix App Development and Integration

I need a skilled Mendix consultant to develop a new app and integrate it with other systems.

Key Requirements:
- Develop a robust Mendix app from scratch
- Update existing features to enhance performance
- Integrate the app with various external systems

Ideal Skills and Experience:
- Proven expertise in Mendix app development
- Experience with system integration
- Strong problem-solving skills
- Familiarity with performance optimization

Please provide examples of similar work done and an estimated timeline.

Edit:
I have a legacy system in Magic XPA w Oracle database and want to migrate it to the web.

Integrations: Resend for mails, Stripe for payments, ISO 20022 payments, Swedish bank payments BGMax Autogiro, Swedish payment system SWISH

The application is a Membership system for national associations to manage memberships, subscriptions , and donations.