We are doing the packing of units in presence of the client representative.
The packing work is taking place in presence of the client representative.
I assume you intend to use the present continuous tense and active / passive are not important. The two options are fine until you reach 'presence'. This requires 'the' in front of it, while I assume the representative is the representative OF THE client, therefore we need an apostrophe.
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I assume you intend to use the present continuous tense and active / passive are not important. The two options are fine until you reach 'presence'. This requires 'the' in front of it, while I assume the representative is the representative OF THE client, therefore we need an apostrophe.
E.g.
The packing work is taking place in THE presence of the client'S representative.