PHP syntax error: unexpected '' (T_ENCAPSED_AND_WHITESPACE), expecting '-' or identifier (T_STRING) or variable (T_VARIABLE) or number (T_NUM_STRING)

This error usually happens when you try to reference an array with quoted keys within a string without using the curly brace syntax.

So you may be trying to do something like this:

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echo "$arr[ 'foo' ]";

// or

echo "$arr[ 'foo' ][ 0 ]";

This will only work if you use the curly brace syntax like this:

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echo "{$arr[ 'foo' ]}"; 

// or

echo "{$arr[ 'foo' ][ 0 ]}";

or otherwise use concatenation like this:

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echo "..." . $arr[ 'foo' ] . "...";

// or

echo "..." . $arr[ 'foo' ][ 0 ]. "...";

Why use the curly brace syntax

The curly brace syntax is also known as the "Complex Syntax" because it allows PHP to parse complex expressions inside strings.

So while a simple scalar variable can simply be used without the curly braces within strings, arrays with quoted keys qualify as a complex expression in PHP and if you want to use it within a string then you must use the curly brace syntax.

For more information, check the official documentation on the Complex(curly) syntax.

Hope this helps!🙏