OPD reacts readily with acetic acid, for example, giving 2-methyl benzimidazole. I made this experiment several years ago. With lactic acid the product must to be 1-hydroxyethyl benzimidazole. If you heat mixture of these two compounds, you must receive crystals after cooling. Cool reaction mixture and wath for the crystals. I cannot give you another advice at this moment.

Jadhav,

Have you tried the reaction in the presence of coupling reagents. See, attachment

You may use 2-acetoxypropanoic acid instead of lactic acid if the reaction did not go well.

Good luck