How to connect tcpdf correctly (prescribe paths)?

Question

PHP

And laughter and sin, but at point blank range it is impossible to connect TCPDF...
Warning: require_once(tcpdf/tcpdf.php): failed to open stream blah blah blah...
Two methods side by side:

public function pdf2(){
require_once( "tcpdf/tcpdf.php" );
}
  public function generate_pdf(){
  	require_once( "fpdf/fpdf.php" );
}

FPDF is working, but TCPDF is not in any ... I climbed in the configs, but does not react to changes in any way ...
For the first time I encounter this ...
How to connect it?)

Answer 1

As an option:
write echo __DIR__ in the code (to understand which directory to write the path relative to):
and then relative to it - write all the paths through /../../