[Isi]

 I'm trying to learn a process of nontoxic electroplating from a book which
suggests to use indium(III)  with chelating agent e.g. sugar alcohol

To quote from the page:
"Indium as In3+ :  Stable in alkali media with a solubility bottom limit for the molar ratio between In : chelating
compound = 1:5
* The chelating compound may e.g. be a sugar alcohol"

My request is how to make the In3+ from solid metal Indium.

[chenbeier]

You have to dissolve Indium in hydrochloric or sulfuric acid.

2 In + 6 H⁺ => 2 In³⁺ + 3 H₂

[Isi]

You have to dissolve Indium in hydrochloric or sulfuric acid.

2 In + 6 H⁺ => 2 In³⁺ + 3 H₂

Thanks @chenbeier , but wouldn't i have to still get rid of the chlorine or sulfur
in the solution so they wont disturb the remaining process? I mean I believe
you don't really get In3+ as instructed, but InCl3 or so, isn't that right?

[chenbeier]

If you have a cathion here like  In^{3 +} you will have every time some anions like Chloride, sulfate or others. It will not exists alone.

In plating copper for example CuSO₄ is used. The anode is copper for dissolving the copper what on the cathode is plated.