Hi @lockyjay,
Thank you for your question and welcome to the Bunnings Workshop community, it is fabulous to have you with us.
You should start by cleaning the post thoroughly with a scourer and 30 Seconds 1L Outdoor Cleaner Spray to remove any dirt, grease or grime that has built up on the surface over time.
Once cleaned, you should give the whole surface a quick sand with 180 Grit Painted Surface Sandpaper Roll, paying close attention to the areas that have chipped away.
Now the prep work has been completed, I'd suggest using Dulux 1L Metalshield Epoxy Enamel Gloss Paint Vivid White as it is designed for use on metal surfaces and does not require additional priming.
You can apply this with a paint roller with a short nap such as this UNi-PRO 100mm 4mm Nap Little Ripper Microfibre Mini Roller Set.
Apply one coat, allow it to dry and assess the coverage. If you are happy then you can stop here, if there are some patches that you aren't happy with, give them a quick sand and then apply a second coat.
You might like to check out How To Paint Metal for some additional guidance.
Let me know if you have any further questions.
Jacob
