If this is paid work and invoiced you better have a paper trail of proof to who designed it and takes responsibility otherwise it still falls at your feet, imagine is someone is injured or worse, do you expect them to put their hands up to possible dangerous installation practices or point the finger at you showing your invoice.
If you are invoicing it it would be an idea to make it part of the invoice declaring no responsibility for design or safety making it clear it was requested, this would not remove you from and possible legal action because unless you have a full paper trail to this the responsibility lies on you to assess any requests meet standards applicable, so tread carefully I
This is intended as a constructive comment. Where possible I would have fused down the 20 amp circuit for the coil. Then one MCB safely isolates the lot. It sounds as though you'd have to turn off two MCB's for everything at the contactor to be safely isolated?
i did consider that option, I don’t regularly install contactors and seen it done that way a few times before. Will take on board though