Cannot backup using hotspot???

Why can I not backup my iPhone 8 using my iPad Pro's was h hotspot as my required wifi connection? (why the required wifi anyway????, that is ridiculous) I have plenty of hotspot data on my ATT account, as each device has it's own unlimited* data package, as well as it's own 30gb hotspot data package (of which I have used less than 2gb of the iPad Pro's hotspot data so far in this cycle)

For the time being, this is my only option to connect to the internet, as I am in a rural area, without a vehicle, job, or any form of assistance, public or otherwise, so please refrain from suggestions such as using public wifi or contracting through an isp to get broadband service.

Honestly, it's a pretty overwhelming situation to find oneself in, especially when the catalyst was a surprise divorce after thirteen years. Needless to say, I am in a bind, and have got to be able to back this phone up, as it is all I have right now, and I do not know when, or if, I will be able to get another. Thanks in advance!