Adding multiple values to an associative array in PHP in one call

Try this:

$post_values = array( 
    "x_login"           => "API_LOGIN_ID", 
    "x_tran_key"        => "TRANSACTION_KEY", 
); 

$array2 = array(
    "x_version"         => "3.1",  
    "x_delim_data"      => "TRUE",  
    "x_delim_char"      => "|",  
    "x_relay_response"  => "FALSE",  
    "x_state"           => "WA",  
    "x_zip"             => "98004"  
);

$result = $post_values + $array2;

Caution however: If the key already exists in $post_values it will not be overwritten.

In order to keep things nice and clean and in this case, simple, you might be better off using array_merge( )

I personally declare any arrays at the top of my class file, in order to make them globally accessible, only because I tend to keep methods free of array declaration (OCD I guess!)

So for me I have an example that might help you, it's something that works for me when needed to add/merge two arrays together:

protected $array1 = array (
  'basic'   => '1',
  'example' => '2',
  'for'     => '3'  
);

protected $array2 = array(
  'merging'     => '4',
  'two'         => '5',
  'associative' => '6',
  'arrays'      => '7',
  'mate'        => '8'
);

Then within your class file, you can use these arrays or any created arrays and merge whenever you want:

public function ExampleOne() 
{
  $firstArray = $this->array1;
  print_r($firstArray);
  
  $secondArray = $this->array2;
  print_r($secondArray);

  $merged = array_merge($firstArray, $secondArray);
  print_r($merged);
}

Each print_r( ) will give you a print out in the console of the data/created array. This is so you can view for yourself that everything has been created correctly and each key has its associated value (check the PHP man pages for a definitive explanation of print_r( ) ).

So, the first array will/should showcase this:

Array
(
  [basic]   => 1
  [example] => 2
  [for]     => 3
)

The second array will/should showcase this:

Array
(
  [merging]     => 4
  [two]         => 5
  [associative] => 6
  [arrays]      => 7
  [mate]        => 8
)

And the array_merge( ) operation will create the final array, which will/should showcase this:

Array
(
  [basic]       => 1
  [example]     => 2
  [for]         => 3
  [merging]     => 4
  [two]         => 5
  [associative] => 6
  [arrays]      => 7
  [mate]        => 8
)

Of course, you don't always have to place/create your arrays at the top of the class file and when needed you can obviously create arrays within a single function if they are only needed/used within there - what I showcased here was just something I had done recently for a project at work (with the data in these arrays being example data of course!)

array_push() will accept an array to be pushed.
But array_merge() may be more what you want.

You can try using the following function: array_merge

You can also use the spread operator:

$post_values = [ 
    "x_login"    => "aaa", 
    "x_tran_key" => "bbb", 
];

$dataToAdd = [
    "foo" => "abc",  
    "bar" => "def",  
];

$result = [
    ...$post_values,
    ...$dataToAdd
];

print_r($result);

Which results to:

Array
(
    [x_login] => aaa
    [x_tran_key] => bbb
    [foo] => abc
    [bar] => def
)

A simple method to avoid complications and mixups, simply use +=

Example:

$data = ["one" => 1];
$data += [ "two" => 2 ];
$data += [ "three" => 3, "four" => 4];
print_r($data);

Result: Array ( [one] => 1 [two] => 2 [three] => 3 [four] => 4 )