how to foreach loop in multidemensional array in php

i am new to php and want to understand the foreach loop. sorry if it is an offtopic and was earlier discussed, but i found little help from other posts.

below are 2 different arrays and the loops used for them to fetch out the keys-values (the first called $size is pretty easy and I have no problems with it; the second called $size2 loops thru an array, but i see error messages in the browser – please suggest what i did wrong):

one level array:
$size = array(
    "day" => "friday",
    "place" => "office",
    "task" => "smalot",
);

foreach loop to fetch our key-values from $size (it works fine):

foreach ($size as $key => $value) {
    echo $key . "=>" . $value . "";
}

two level array:

$size2 = array(
    "day" => "friday",
    "place" => "office",
    "task" => "smalot",
    "level2" => array(
        "place" => "desk",
        "laptop" => "lenovo",
        "coffee" => "black",
    )
);

foreach loop to fetch our key-values from $size2 (it works not properly):

foreach ($size2 as $key => $value) {
    echo $key . "=>" . $value . "<br>";
    
    foreach ($value as $subkey => $subvalue) {
        echo $subkey . "=>" . $subvalue . "<br>";
        }
}

the result of the foreach loop for $size2 is below:

day=>friday

Warning: foreach() argument must be of type array|object, string given in C:xampphtdocspdfparsersize.php on line 35
place=>office

Warning: foreach() argument must be of type array|object, string given in C:xampphtdocspdfparsersize.php on line 35
task=>smalot

Warning: foreach() argument must be of type array|object, string given in C:xampphtdocspdfparsersize.php on line 35

Warning: Array to string conversion in C:xampphtdocspdfparsersize.php on line 33
level2=>Array
place=>desk
laptop=>lenovo
coffee=>black

if i uncomment the inner loop, then i can fetch the key-values from upper array:

foreach ($size2 as $key => $value) {
    echo $key . "=>" . $value . "<br>";
    
//   foreach ($value as $subkey => $subvalue) {
//        echo $subkey . "=>" . $subvalue . "<br>";
//    }
}

result:
day=>friday
place=>office
task=>smalot

Warning: Array to string conversion in C:xampphtdocspdfparsersize.php on line 33
level2=>Array

but the goal is to fetch upper and inner key-values from an array and see no error messages. what shall i do? thanks again!

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