The set of rules for naming a coordination compound is:

$1$. Name the ligands, put in alphabetical order.

$2$. Add prefixes for ligands that appear more than once.

$3$. Name the metal

For Cationic complex- write metal name.

For anionic complex- write metal prefix $+\mathrm{ate}$.

$4$. Add oxidation state in Roman numerals.

$5$. As separate word, write "ion", if not neutral, or list counterions (positive first, negative second).

The $\mathrm{IUPAC}$name of the compound ${\left({\mathrm{NH}}_4\right)}_2\left[\mathrm{Ni}{\left({\mathrm{C}}_2{\mathrm{O}}_4\right)}_2{\left({\mathrm{H}}_2\mathrm{O}\right)}_2\right]$ is Ammonium diaquabis (oxalato) nickelate $\left(\mathrm{II}\right)$.