Syntax for patch on cmd line?

Running M1, I generated a patch from IDEA for a handful of files. I took the patch generated and tried running it against the same repository on another machine. I can't get patch to accept it, so am wondering what format/flags IDEA is using to generate the patch file.

Running patch 2.59 on Ubuntu.

Have been trying various permutations, like
>patch -i Mantis_6139.ptc -u --dry-run
can't find file to patch at input line 3
Perhaps you should have used the -p or --strip option?
The text leading up to this was:
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have tried
-p, --strip flags, with and without -u

Haven't found the right combination.

Tips?
Patrick