The locating recess looks shallower. I've sent the confirmed drawing and delivered-label photographs together, with the bracket still off the arm. I have not tried to make it seat

Ask for the applicable delivered-interface drawing and a comparison of the complete mating arrangement. Include fasteners and locating features, with your installer reviewing it. A photograph can identify the concern without establishing the dimensions or whether an adaptation is acceptable.

Seller's technical contact supplied a drawing and confirmed the recess differs. They propose a replacement bracket rather than providing a comparison for the one we ordered

Who would own the replacement design and its effect on your fixture position?

Keep the original configuration as a separate option to ask about. The replacement may be workable, but Omar should not have to accept design responsibility simply because it is the first concrete proposal offered.

Thanks Maya, that ownership question mattered. Seller has now offered to supply their reviewed bracket assembly, but our installer still needs its fixture-position and mounting comparison. No offer accepted and no fitting authorised

Does purchasing have the same outstanding comparison recorded before responding to that offer?