the itunes store is unable to process purchases at this time

It could be that Apple have made changes that break behaviour in 12.6.5.3, intentionally or not. See https://forums.macrumors.com/threads/itunes-can-no-longer-be-used-to-manage-apps.2283439/. It is worth noting that the support document that hosts 12.6.5.3 Deploy apps in a business environment with iTunes - Apple Support has been archived for some time, meaning Apple aren't actively supporting this workaround any more.

tt2

My company have this issue as well. As far as we can say (as more then 100 PCs and more then 5.000 devices are affected) its a change on the iTune side ... locks like the blocked the old Itune Client and blocked the way we push apps to the devices...

By the way new re-downloads are blocked now (the button is greyed out):

Зачем я должен ждать пока закачается программа если она у меня есть на ПК. И как быть с теми программами которых нет больше в магазине если как вы говорите я их удалю откуда мне их качать ерунда полная ......

Why should I wait until the program is downloaded if I have it on my PC. And what to do with those programs that are no longer in the store if, as you say, I delete them from where I download them is complete nonsense ......

It's been broken all week. So now I have over 100 apps that i need to individually delete, then re-download. It's very messy. Apple should fix it. I applauded them for keeping 12.6.5.3 working, but when i went to update that posting to say 12.6.5.3 was working again, I couldn't add anything.

Me too. I had to erase all content on my iPad 4 with ios 10.33 because it's so slow. Now I can't re-download my apps that I paid for already. Note: this was my first iPad. I have 5 ipads now and latest iPad is ipad pro 2020 but I use them all for church music. Now I'm down to one because of this stupid error. FIX IT APPLE!

It's still broken after all this time. The only work around I have is still a bit messy, and I'm worried that someday I erase the apps and i won't be able to download the updates.

Here's what "seems" to work for me thus far:

Run "Check for Updates", select all and then delete all from my library, but i usually "keep the files" and not fully delete completely. Then go run check for updates again, it should not show anything. Then i usually do "Check for available downloads" to see if there are any downloads, but it says none. THEN, I select the "Purchased" option under Account, and it eventually pulls all the apps that I just deleted earlier. I can click individually on every single one that is prompting to download, or if there are a lot of them, I usually can go to the bottom right corner where it says "Download All" to do most all of them together. I say "most all" because the automatic batch download stops if it hits an App that it can't download (there are usually 3 for me: Apple Books, Apple Podcasts, and Find My Friends which can only be downloaded directly on each iPhone/iPad), then I have to select the rest of the Apps individually to download the rest of them. It's messy, but it does seem to keep my library up-to-date and I can further update my iPhones/iPads from iTunes from there. Apple should fix all this for those of us loyal customers who own multiple iPhones/iPads and need to update them all together.

Apple aren't listening here. Use Feedback - iTunes - Apple.

tt2

Try rebooting your router and computer and see if that has any impact. Status pages look good right now.

tt2

Let this version of iTunes work as before .

Пусть эта версия iTunes работает как раньше .

I am having the same issue with iOS 10.3.3

It worked when I went to "purchased" section. Soooooo annoying!!!

It looks like they fixed it late last week! Thank you Apple!