How do I reinstall application accidentally deleted also no longer available on App Store?

If anyone can possibly help me I would be eternally most grateful!

in March this year I accidentally deleted my all-time favourite app Postale (or anyway, was opening it when it suddenly disappeared) and am my wits’ end as to how to get it back on my phone. I’ve had it there since 2016 and it was working perfectly in March this year.

(I cannot find any more modern equivalent that is in the same league or even close, so the help I need please is to retrieve it).

It does not appear either in my app library or - strangely - purchase history and is no longer in the App Store 😫

It was a free app to download and to use:

I have read that it is possible to restore an individual app through iTunes using the “apps” tab on any OSs before 12.7.

i still have my former (slow, but perfectly functioning!!) iMac (20” early 2009) with El Capitan (10.11.6.20). However, when I connect my iPhone 11 Plus (iOS 17.6.1) an error message on the computer advises me that I need to update the iPhone software for it to connect to iTunes.

When I try to do that, it gives me a message saying the software can’t be downloaded because is not available from the updates Server.

woe is me!! What oh what do I need to do to restore my belovèd Postale app, and why has it been suddenly removed from the App Store?

I have been unable to trace and contact the developer to check.

Please, please can you clever folk help me by whatever means are necessary to get it back.

Any help at all to that so-longed-for end would be just wonderful.

Thank You for any help you are able to provide.

Jackie

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