向客户解释发货晚的原因,不知如何写成英文,求帮

i am sincerely sorry for the late of delivery,but making the AB ,product code ,take a long time , however ,i'll delivery the goods asap.

万分感谢

We are really so sorry that we he to get more time to delivery goods for AB items complex production,
but we'll do our best to delivery them ASAP and keep you informed with everything.

Your kindly understanding would be highly appreciated.Thanks

多谢指教

sorry to inform you the goods will be delayed x weeks.the ETD will be xxxx.We will do our best to deliver the goods ASAP.
我感觉不要给客户说原因，只能越描越黑。你说产品工艺复杂，客户会说你一始就应该知道你们的产品工艺程序而不是到最后再告诉我，而且复杂不复杂和我没有任何关系

we are really sorry for the delay. for we tooke more time to produce Part AB , it 's more complicated than we expected.   below is our new schedule for this shipment : ETD Chian  ---   ETA ----.

i am really sorry for delay your time,  cause the process of producing AB is very complex. So, it takes some time. But pls don't worry dear, once goods ready, we will send you immediately.    FYI

For some reason, the develivery of AB is delayed, we'll try to make it the soonest possible.

time consuming ,delayed, ...

I am really sorry date of delivery was overtime as the Production processing is very complex for item AB, i will delivery the order ASAP.