How do I bring back my lost space after trying to merge APFS partitions?

How can I merge primary APFS partition with other empty APFS partition?

After reading and following the above, I got stuck on the eraseVolume "Free Space" and now that space seems irrevocably lost. Did apfs resizeContainer but got Error: -69743: The new size must be different than the existing size and it seems that my 2TB physical drive can recognise only 999.4GB…
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any help?