[ Please Help ] - Submitted URL seems to be a Soft 404 Issue - How can I fix it?

Dear SEO gurus,

I received this message from Google Search Console as the reason of one of my sites not being indexed:

"Submitted URL seems to be a Soft 404"

May I know how to fix it?

Thanks pals !

I found this in qwant:
https://wp-rocket.me/blog/google-soft-404-errors-fix/

tazarbm said:

I found this in qwant:
https://wp-rocket.me/blog/google-soft-404-errors-fix/

Click to expand...

Thanks for the tip mate.
I've read about this quite a bit already and cannot get to a definitive solution.
This usually happens when your page(s) have thin content, which is not my case.
I tried indexing services and they work for a while and suddenly the pages get unindexed once again.
It's weird, but G has gone weird for a while now.

If someone else knows how to fix this, please share!