IF, ELSE IF, ELSE with date differences in PHP

Question

I’m trying a condition on ELSE IF that’s gone wrong, I’ve done some pretty similar things and I really don’t know what it is...

I have a table on my system, where it displays some information for the user, within it, has a field called payment, I had to put this field as input like text, why the user can put or "PENDING" or put the date of payment, and so I ended up leaving the input as text.

Another field is called emissary where is the type date and I need to compare days with this field.

Conditions are working, minus the ELSE IF.

I need you to take the field emissary spend 30 days and the countryside payment is pending, it uses a certain class...

I tried to do this by picking up the difference of years/days/months from the date of emissary compared to the current date, and played on one condition.

Let’s go to the code:

<?php

                $sql = "SELECT * FROM emissao_nf";

                $resultado = mysqli_query($con, $sql);

                while ($cont = mysqli_fetch_array($resultado)) {

                $prazo = new DateTime ($cont['emissao']);      // Data do banco em DateTime
                $hoje = new DateTime();                        // Data atual em "DateTime"
                $intervalo = $prazo->diff( $hoje );             // Pegando a diferença de anos, meses e dias

                if(substr_count($cont['pagamento'], 'PEN') > 0){ 
                $mostra="status-p bg-warning"; //Pendente, amarelo

                }elseif(substr_count($cont['pagamento'], 'PEN') > 0 && $intervalo->m >= '1') {
                $mostra="status-p bg-danger";  //Passou 30 dias e está pendente, vermelho

                }else{
                $mostra="status-p bg-primary"; // Data de pagamento, azul
                }

                echo"
                <tr>
                <td><span class='".$mostra."'>".$cont['pagamento']."</span></td>
                </tr> 
                "; ?>

The ELSE IF does not work, not page error or anything... Can anyone help me? I think it’s wrong that I’m using a type text for dates, however, I don’t know what I can do.

In this print, the idea would be that it was "PENDING" but in red... Today is day 09/06/2020