Here is my method of soldering the Anderson PowerPoles easy and cleanly.
Start with tinned cable ends.
Place the APP contacts on the work surface oriented the way they will be placed in their plastic housings (this is with the split on top).
Touch the CLEAN tip of your soldering iron on the contact’s barrel.
When sufficiently hot, start feeding solder in the contact’s hole. How much you will find by trial and error.
While you are still holding the soldering iron on the contact, insert the cable end.
Some melted solder may ooze out.
Remove the soldering iron, let the contact cool and clean the rosin.
An added benefit comes if you cut he bare wire just a bit longer. Since the cable hardens, it affords a better purchase and manipulation when installing the contacts in the housings.
Just like that!