Modal to prepare users for changes in payment system

I'm wondering if you could help me to gather some ideas.

Basically, one of our products overseas has to make fundamental changes to its credit card deposit system due to a variety of problems incl. a change legal requirements that will require us to implement a 3rd party provider that handles the credit card transactions (additional and new step in between).

Unfortunately, this change will require a last minute implementation (not ideal) and our customer base will face this change from one day to another. No doubt that some of our customers will be rather confused by that and are potentially worried being scammed as the 3rd party provider has a complete different look/feel than actual site (apart from a smaller logo from us in the upper corner). This could've a direct impact on the revenue of the business and worries me quite a bit.

Ideally we would've been able to prepare our customers upfront, but we had no chance to prepare for this.

Initial idea:

Showcase a modal after engagement of the credit card deposit button to prepare users what's coming up next. This modal may not only contain textual information about what changed and why but potentially also displays an actual image of the site that a user will encounter. Unfortunately, we can't introduce any changes to the 3rd Party layout/step.

Qs:

  1. Do you think that's a valid approach?

  2. What information would a user potentially want to see within the modal? How could we phrase the text so that it's clear what's going on?

  3. How can we address this in a way that is still perceived to be positive (Improved security, additional credit cards being allowed) but also not entirely lying about the fact that it's potentially an annoyance for our customers? Something along the lines of ‘Good news! We introduced a new credit card deposit system…’ Maybe acknowledgement that it ‘Improves your security’ and that it allows for ‘multiple cards to be accepted’.

I want to shine a positive light on this without hiding the fact that it may be an annoyance for customers who were very much familiar with the previous process.

Any ideas at this point are quite useful.

Sorry for bugging you with this stuff, guys. Thanks for your help.

Thanks! :-)