SA ISP proxy blocking card payments

[Killerpup]

Hi guys, I'd like to understand how a ISP using a proxy can block a payment widget on a website?
I'd also like to know how to test this and what tools I can use?
Take Rain as a example, I am under the impression Rain makes use of a proxy and for certain sites and services, it blocks them.
Why would this happen and how? How would I identify that?

 

[Tim_vb]

Peach’s card widget is being blocked by Rain

I tested using a few different ISP and it fails on both their 4G and 5G networks - might be their DNS