Choosing a solution for creating a tour operator loyalty program?

Question

ERP

I work as an analyst in a major international tour operator, with a focus on Russia, Turkey and Eastern Europe. We need to rework the loyalty program, which exists, but does not actually work. In the market of tour operators in Russia, no one has a sane loyalty program at all. Now it exists in the form of a website, a legacy application written in Delfi, and an application for entering client data. At a minimum, all this needs to be transferred to an adequate infrastructure, and the functionality should be further developed. Therefore, I would like to know from knowledgeable people what specific tools can be used for this and what steps to take so as not to reinvent the wheel. Initially, it was planned to give all this to contractors (conditional Mindbox), but the crisis and the desire to save money are pushing the business onto the path of its own development, which seems to me not entirely correct. In the company, almost everything is on the Microsoft and .Net stack, crm Dynamics 365 on premise with reduced functionality. There is actually no BI analytics in its modern form either, this is another pain. Do everything inside a big monolith or create a new service? What part to take away to the new service? How should the monolith and the new service interact?
I myself have experience with Mindbox and RX Loyality.
I was interested in this case with iDempiere https://habr.com/en/post/554246/comments/ .
The stack can be elected, now its own development department is actually being created from scratch and there are no clear outlines yet.