user71421: I'm using TTGO ESP32 and I've got an MFRC522 from AliExpress.
I've soldered connector pins to the board itself (both for ESP32 and MFRC522) and I'm using jumper wires female-to-female to connect themselves.
However, using an example sketch (DumpInfo) from miguelbalboa's RFID library, it says communication failure and scanning 3 different key cards or the key fob doesn't output anything.
Firmware Version: 0xFF = (unknown)
WARNING: Communication failure, is the MFRC522 properly connected?

This is my current pinout scheme:
(MFRC - ESP32)
SDA (SS) -> 33
SCK -> 25
MISO -> 27
MOSI -> 26
RST -> 32

And, of course also GND to G and 3.3V to 3.3V.
I've also tried SDA and SCK to connect to 21 and 22, respectively but no luck.
Though I have a DS1307 RTC module and microSD card adapter module and connected accordingly and it's working fine, by using Dupont wires, with the same method.
A manufacturer's defect or still I'm making an error somewhere?
You can see TTGO's ESP32 pinout diagram and also a picture of MFRC522 here  wired using jumper wires. I may be using (again) the wrong pins. The red LED on the MFRC522 is stable, though.
Thank you in advance.

user71421: UPDATE!
The issue has been fixed, just after finding this stackoverflow answer by bat macumba. I'll leave the question here, in case someone stumbles into the same problem.

71421: <p>I'm using TTGO ESP32 and I've got an MFRC522 from AliExpress.</p>
<p>I've soldered connector pins to the board itself (both for ESP32 and MFRC522) and I'm using jumper wires female-to-female to connect themselves.</p>
<p>However, using an example sketch (DumpInfo) from miguelbalboa's RFID library, it says communication failure and scanning 3 different key cards or the key fob doesn't output anything.</p>
<pre><code>Firmware Version: 0xFF = (unknown)
WARNING: Communication failure, is the MFRC522 properly connected?
</code></pre>
<p>This is my current pinout scheme:</p>
<pre><code>(MFRC - ESP32)
SDA (SS) -&gt; 33
SCK -&gt; 25
MISO -&gt; 27
MOSI -&gt; 26
RST -&gt; 32
</code></pre>
<p>And, of course also GND to G and 3.3V to 3.3V.</p>
<p>I've also tried SDA and SCK to connect to 21 and 22, respectively but no luck.
Though I have a DS1307 RTC module and microSD card adapter module and connected accordingly and it's working fine, by using Dupont wires, with the same method.</p>
<p>A manufacturer's defect or still I'm making an error somewhere?</p>
<p>You can see TTGO's ESP32 pinout diagram and also a picture of MFRC522 <a href="https://imgur.com/a/qnUY7iK" rel="nofollow noreferrer">here</a>  wired using jumper wires. I may be using (again) the wrong pins. The red LED on the MFRC522 is stable, though.</p>
<p>Thank you in advance.</p>
 71421: <p><strong>UPDATE!</strong>
The issue has been fixed, just after finding this <a href="https://stackoverflow.com/a/64998779/5847989">stackoverflow answer</a> by bat macumba. I'll leave the question here, in case someone stumbles into the same problem.</p>
