Howdy from Montana, "GamerCore"! How 'bout a "first name" to call you, even if it's an alias?
I've had the ZTE Blade v8 Pro for three days now; and, other than the issues that I've already resolved (thanks in part to your excellent suggestions), my main issue, really the only one, right now is that I transferred over a SanDisk 128 gb SD card from my Amazon Fire HD 8 tablet, and I can't get the Amazon Prime Music files that I don't own (that Amazon now allows being downloaded with protection so you can't get the digital albums for free otherwise), and that are downloaded to said SD card, to show up in the Amazon Music player under Offline Music, though all of them showed up just fine in the Fire HD 8 tablet (and still would if I put that same SD card back in the tablet).
I shut down and restarted the ZTE Blade v8 Pro, and then about 648 songs showed up in Offline Music, about half of them songs that I purchased. But I have literally a couple of hundred albums on that SD card (it is almost full), and thousands of songs. Regardless of whether it's a Fire Android device or not, the Amazon Music player should be able to read the protected song files that were protected by Amazon, and all of them should show up in the player. Yes, I refreshed my music, and I thought over time, with wireless on (to perhaps check the protection with Amazon's website), that the songs would eventually populate from the SD card, like on the Fire tablet, but they don't appear to be doing so.
I can understand that, because of the protection of the songs, they wouldn't be able to be read, shown and played on any other music player, but in the Amazon Music app, they should show up and play just fine. I phoned Amazon, and finally got someone in the U.S. who claimed to be knowledgeable on Amazon Music, but she was extremely rude and I don't believe she knew what she was talking about on Amazon Prime Music.
Do you have any idea how to correct this issue, or could you find out, because I'm relatively sure that a lot of people are likely having this issue? Yes, I know, as the rude gal at Amazon suggested, one can re-download all of the albums to the SD card, but with almost 128 gb of data and so many albums and songs, it would take far too long (days) to do that, so I'm not going to go through all of that; because, for one thing, I'm pretty sure there's a relatively easy fix for this (which I haven't been able to find online as yet).
Oh, I also safely removed the SD card from the phone, and put it back in, before rebooting the phone. And, it looks like by the time you read this, I will have also tried safely removing the SD card, rebooting the phone with it out of the phone, and putting it back in after restarting the phone.
Btw, it turns out that the exactly 648 songs showing up in Offline Music, are ALL songs that I purchased; so, NONE of the Amazon Prime Music "non-purchased" songs on the SD card are showing up in the Amazon Music player app right now, no matter what I've tried to do so far to fix the issue.
Otherwise, so far this appears to be an excellent device, and it's of course not ZTE's fault concerning this Amazon Prime Music issue. I haven't obtained a SIM card yet, so I can't speak to how the phone works for placing and receiving phone calls, texting and data from the cell system. What SIM card do you recommend for the lowest price and month-to-month cost? I really only want to have the SIM for emergencies, usually keeping it out of the phone most of the time, so I want a carrier service that I only have to pay for what I use, without shutdown of the SIM card due to inactivity, without having to pay too much up front, and without the service account expiring for lack of use. Any good suggestions on this? I've looked online, but there are so many choices that it's so confusing and overwhelming for me (I'm physically, but not mentally, disabled; and I am very intelligent), and the reviews make so many of them sound like bad investments; or like, in the case FreedomPOP, scams; or, the coverage area doesn't include my area for data as well as calls and texting (Ting), the northwestern Montana, Flathead County/Valley area, and the north end of same. Which reminds me, yes, I want calling, text and data.
Summarizing my questions in case you've forgotten them already

) ....
1.) Fix for Amazon Prime Music being completely read and playable from the SD card to the Amazon Music player app.
2.) Best recommended SIM card and service carrier for "not-all-the-time", and intermittent, use.
3.) Any other suggestions you might have and want to share, related or not to my issue(s) [inferred though not asked above].
Thank you, "GamerCore", for all of your consideration of, and assistance with, this entire matter.
Sincerely (and Cheers!), from,
Wolf (my real, legal middle name, and what I go by)