XML request payloads can't contain tags of the same name

[LukeCarrier]

Because of the way SimpleXML places significance on the tag name and uses it as an index for elements, elements with the same name cause the parsed result's structure to not match up to the parameters.

For instance, the following structure:

<request>
  <multi>
    <single>0</single>
  </multi>
</single>

(correctly) gets interpreted as the following:

[
  'multi' => [
    'single' => 0,
  ],
]

With multiple single elements:

<request>
  <multi>
    <single>0</single>
    <single>1</single>
  </multi>
</single>

the generated output instead looks like:

[
  'multi' => [
    'single' => [
      0,
      1,
    ],
  ],
]

This causes parameter validation to fail.

For the time being, the mitigation is to use unique names for the single elements, e.g. single-0, single-1.